So how would this affect everything else? Smoking is a social event. People strike up conversations on their smoke breaks. The members of The Beatles probably bonded a lot over cigarettes, so they no longer had that same camaraderie. If J.K. Rowling was a smoker, she might have come up with the basic idea for Harry Potter on a smoke break. Just as the now little-known John Lennon was never shot, the millions of people who died from smoking-related illnesses never got lung cancer in the first place.
WMG / Yesterday (2019)
The reason Jack remembers the BeatlesDuring the 12-second blackout, Jack is hit by a bus and probably would have died had he not been wearing a helmet. This means he came close to death at the exact moment the world changed. So maybe the shock associated with such a traumatic incident is what allowed him to retain the knowledge of the Beatles (and other things that no longer exist), as opposed to the rest of humanity who were just going about their daily lives. Of course, the fact that Leo (from Moscow) and Liz (from Liverpool) also remember the Beatles suggests that they experienced some sort of trauma during the blackout too like a heart attack or a car accident.
Jack goes on to write Harry Potter after the end of the movieAfter giving up his music career and getting together with Ellie, Jack mentions that he feels like Harry Potter after he defeated Voldemort. Ellie responds, "Who?" prompting Jack to realize that Harry Potter doesn't exist in the new timeline. It's played as a throwaway gag, but it's easy to imagine Jack reasoning that being a writer, even one as rich and famous as J.K. Rowling, is not nearly as demanding as being a music star, and furthermore that writing is a career he could easily do from Lowestoft (other than book tours and such). Admittedly, there is no proof Jack remembers Harry Potter as well as he does The Beatles, but he could definitely have given in to a lesser temptation.
In reality, this is a movie about what would happen if cigarettes didn't existSomeone wished, for the sake of health, that cigarettes disappeared from the face of the earth. The wish came true, and "cigarette" is nothing more than a town in France. The health-conscious wisher also wished Coca-Cola out of existence, but forgot about Pepsi and other soft drinks.