Space Opera, once the dominant sub-genre of Science Fiction, has declined considerably since The Eighties. The reason for this is twofold. Firstly, the end of the Cold War also ended the Space Race between the Soviet Union and the United States, leading to a period of stagnation. Secondly, around the same time an unexpected explosion in computers and bio-technology occurred. These two factors caused futurists and Sci-Fi writters to stop looking at Space for inspiration, and look instead to genetic engineering, cloning, cybernetics, virtual reality, and artificial intelligence, hence the dominance of Cyber Punk and its derivatives. It's only in recent years, with the over exposure of cyberpunk, nostalgic reconstructionist works of Space Opera (like for example, Mass Effect), and renewed interest in space coming from the discovery of Extra-solar planets that the Genre has begun to recover. Cyberpunk and its derivatives remain on top however.
For much of The Eighties, the cyberpunk literary genre and movement was the new wave in both Science Fiction and science fact, acting as a fertile seed on a ground tormented by efforts to adapt to a changing world where the computer was king and Japan was the new force on the block. However, books like Neuromancer failed to anticipate how a) the internet, cell phones, personal computers and handheld IT devices would become a mundane reality in the life of the average white-collar Joe Sixpack, and b) that the Japanese economic powerhouse would trip over itself in the early '90s. Once "the future" became the present, cyberpunk went from being high-tech to being filled with zeerust, painting a portrait of the future that had stopped being relevant after about 1993 — the main reason why Post-Cyberpunk came to replace it. Not to mention that the virtual reality craze of the late '80s and early '90s simply shelved itself (for now) after failing to provide a holodeck-like experience.
Pulpy Long-Running Book Series aimed at kids, pre-teens, and teens that were published on a steady clip (sometimes monthly) were incredibly popular during the '80s and '90s, both with story arcs and as standalone anthologies, such as The Baby-Sitters Club,Sweet Valley High,Goosebumps,Fear Street,Animorphs, and even the Spin-Off series The Nancy Drew Files and The Hardy Boys Casefiles. Nowadays, books aimed at children are longer, more complex, and are pre-determined in terms of arcs and book number (Harry Potter had 7, Twilight had 4, etc., compared to the previous series which seemed to go on forever.)
This shift in kid-lit came about in an oddly positive way; namely, publishers stopped believing that Readers are Morons. It seemed to be believed that a generation of children raised on episodic television and music videos would only want bite-sized "episodes" of stories instead of longer and more elaborate books. In fact, one of the reasons that Harry Potter was rejected repeatedly was publishers believing that kids won't read long books. However, after one publisher gave the manuscript for Philosopher's Stone to his young daughter, who devoured it in short order and asked for more, they finally realized that kids could appreciate the depth and texture of longer books, and have been focusing their efforts on finding the next Harry Potter.
...and that was books about "elite" high school girls. Following the success of the film Mean Girlsnote Which could be argued, in hindsight, to be an Unbuilt Trope example of the genre due to its examination of the culture of school bullying., books about the lives of incredibly rich, spoiled teenagers became a big market, with one of the more successful examples, Gossip Girl, even being turned into an even more successful TV series. However, it is very difficult to make these kind of protagonists likable or sympathetic, and the books quickly became Snark Bait among actual high-schoolers.
Another reason was most likely the 2008 recession, which made large displays of wealth seem tacky.
Teen Paranormal Romance as a genre largely rose and fell with the success of (and backlash against) Twilight. See that book's entry under "Specific" for more details, many of which applied to the genre as a whole.
Starting in the late '00s and peaking in the early '10s, dystopian and post-apocalyptic fiction became the hot trend in YA literature, chiefly off the back of the success of The Hunger Games. While some Moral Guardians felt that the books were far too dark for teenage readers, said teens otherwise gobbled them up, their use of authoritarian societies as metaphors for high school life resonating with many at the height of both the Great Recession and a national debate about bullying and teen suicides. The Hunger Games itself didn't burn out like Twilight did, but the genre eventually oversaturated YA shelves at bookstores, and a stereotype emerged that the plot of a lesser "YA dystopia" could be summed up as "teenage girls Godwinning their pushy parents and cliquish classmates by comparing them to Oceania". While the film adaptations are just starting to come out, so far they've been mostly met with mixed receptions outside of The Hunger Games (which made a star out of Jennifer Lawrence), and the novels themselves are starting to fade from bookstores.
Gamebooks, which started with the Choose Your Own Adventure and Find Your Fate series eventually evolved into books that actually included combat with Dice. Some books were even published by TSR games (of Dungeons & Dragons fame). Video games can't really have been said to be directly responsible for killing gamebooks but they do provide a non-linear nature that gamebooks can't provide. Also videogames make it harder to cheat, always a spoiler in gamebooks if you turn to the wrong page or intentionally peek at pages that you aren't sent to. And the videogame experience usually promises many hours (even days) of gameplay. Gamebook experiences were notoriously short (as in minutes). The Choose Your Own Adventure books had multiple endings, sometimes as many as 25 in one book. This means that each adventure was rather short. Replay value was somewhat limited to rereading a lot of the same pages, making different choices, and finding different endings, many of which were bad or dull endings. Today, print gamebooks have been replaced by computer based interactive fiction (which could be said to be the Spiritual Successor), and visual novels, although these are more popular in Japan than they are in the rest of the world.
Books of fiction for adult audiences fewer than 300 pages long were quite the industry in the 1970s. Now, books that short simply don't get new publication, and even reprints of giants like Louis L'Amour are thin on the ground.
The Clique by Lisi Harrison is the exemplar of the aforementioned "elite high school girl" series and how that genre declined. During the series' first publication run from 2004 to 2011, it was one of the hottest young adult series around, with many comparing it to Mean Girls in literary form (the series started around the same time the movie came out). Several of the books in the series made the New York Times Bestseller List (though frequently for only a week or so), and it received a film adaptation in 2008 starring a then-unknown Bridgit Mendler. Then, almost as soon as the series reached its conclusion, it just about dropped off the YA radar completely, with Harrison quickly moving on to write other series like Monster High and the spinoff Alphas, both of which faded into near-obscurity as well.
Point Horror was a line of teen-oriented horror novels written by authors like R.L. Stine, Diane Hoh, A. Bates, and Christopher Pike that was popular among middle school students in The Nineties, seen as an "adult" version of series like Stine's Goosebumps. They often had pulpy plots based around teenage girls battling psychos, cults, secret societies, and other malicious forces while dealing with high school life, in a manner reminiscent of films like When a Stranger Calls, Sorority Row, or The Skulls, and were never seen as "serious" literature even by the standards of young adult fiction. While there was once a time when Point Horror books could be found on any teen girl's bookshelf, the series died out and was largely forgotten in the Turn of the Millennium (even as Goosebumps and its ilk remained popular with young readers and nostalgic with older ones), and when it is remembered, it's mostly for its Strictly Formula writing.
Maximum Ride went from a New York Times bestseller (even with talks of a movie adaptation) to near-obscurity due to increased amounts of ass pulls, anviliciousgreen Aesops, and a very poorly done Re Tool to appeal to the Twilight crowd. The final book came out with almost no fanfare. It really says something when its graphic novel adaptation is more well-known and better regarded, to the point of Adaptation Displacement..
The Baby-Sitters Club used to be a smash hit phenomenon with a movie, TV show, and countless other merchandise. Now it's pretty much unknown, mostly due to aging very badly. There have been numerous attempts over the years to republish and/or reinvent the series (prequels, graphic novels, etc.), but all of them flopped badly. The only people still actively reading and remembering the series seem to be snark blog writers.
Browns Pine Ridge Stories: An In-Story example. The author writes in the seventeenth story that "Maybe collecting turpentine has gone out of style," as a result of it being replaced with cheaper and/or more effective substitutes. Though it's worth mentioning that this observation is not entirely true as an article on The Other Wiki shows that it still has uses in some modern day products.