In Star Trek Online, there is a way to get an assimilated tribble. It's cute and hilarious, until you realize that tribbles breed exponentially. Imagine if the Borg incorporated that trait into the Collective. Imagine they already have...
Borg don't reproduce/replicate, they'd find that trait too 'imperfect'. The Borg's quest for perfection tends to lead away from messy biological processes. Plus, just imagine "Who put the Borg drones in the quadrotriticale?"
Then explain the Borg babies the Enterprise crew found in "Q Who".
The Borg assimilate infants, too (they're placed in maturation chambers to develop faster after the first stage). Them being baby Borg was Wild Mass Guessing based on what they saw.
Borg do replicate/reproduce. We just don't see much of it.
Assimilation as it is known now did not exist until First Contact, which subjected the Borg to massive Flanderization. The Borg reproduced biologically and put implants into their babies surgically. The assimilation planned in "The Best of Both Worlds" was likewise going to be a gradual process with some poeple (probably only children) being assimilated and the Borg gradually slowly suberting all aspects of the Federation, as they could not just grab people and assimilate them on the spot like in First Contact. Picard was the first to be assimilated, as his authority and stature made him a good candidate for an intermediary representing the Borg's influence as they conquered the Federation. Their attempt to assimilate the Federation was also shown as exceptional (perhaps due to the Federation's higher technology levels than any of its Alpha and Beta Quadrant neighbors) and that the usual modus operandi was that the Borg showed up in the space of any civilization that had an interesting technology they wanted, took the technology in question, and exterminated the "irrelevant" people making up the civilization. First Contact with the rapid assimilations, Queen, etc. turned the Borg into a caricature of their original selves.
The above wall of text, while having some points, is pure YMMV (as is this post). In some other's opinions, it only made the Borg more terrifying, not flanderized or caricatured in any way.
Actually at first maybe the Borg were not interested in assimilating people, probably because they didn't need them. Only in First Contact where the Borg are really low on numbers do they begin assimilating the people. Now that they are fighting the Undine they probably really need people and are grabbing anyone they can. This is more of a WMG though.
Or in between TNG and First Contact the Borg ran into a race with advanced nanotechnology and assimilated them, assimilating their technology as well. They then adapted it to infect people and turn them into Borg. The full scale implants are installed when they have the chance.
The likely size of the Hobus Supernova. If one were to look on the Galaxy map they would see that both the Hobus and Romulus systems are at least one sector apart from another(which amounts to at least 20 light years). Accepting that just beyond Romulus was where Spock was able to stop the supernova and that the supernova ejected its energy in every direction, how many other worlds were caught in the supernova's path?
None. You learn in the course of gameplay that the explosion traveled to Romulus through Subspace, thanks to Taris.
All those Elachi you were killing through out the Romulan Captain's story arc? Those were probably your former colonists.
And what's worse? When you find out the Elachi are turning the captured Romulans into more Elachi, you slowly realize they're doing exactly the same as the Borg do: assimilate. The only difference is the type of creature they're converted into... biological instead of a cyborg.
From your perspective as a player, you're a particularly awesome character who runs around having adventures across the galaxy, albeit with more action than is normal in the Star Trek shows. But if you think about it from the perspective from all those Mooks you tear through on a daily basis, or all those ships you destroy regularly, you realize that even a Federation Captain might just be one of the biggest killers in ST history. For example, a Romulan T'varo Warbird has a crew of about 150 people. You will probably destroy dozens of these throughout the game, not to mention the large numbers of capital ships (D'Deridexes have a crew of over a thousand) you destroy. None of the famous captains—not Kirk, not Picard, not Janeway, not even Sisko during the height of the Dominion War—have amassed as big of a body count as you have.
Which further makes sense, since it can explain why we never get to see any of the things like the lots of disabled ships the series has, and even non-space-combat sections of the game have, why we never have to deal with escape capsules, why there never is any time between being hit and the ship going critical, and why our character can continue damaging the enemies after respawning from a seemingly total loss of ship and all hands exactly where they left off. ... Imagine the "Repairing" bar from allied spacecraft in story missions.
A much more jarring and difficult to explain problem however was introduced with Delta Rising. Even before Borg could be retrained to serve Starfleet, and even liberated, but with the Cooperative being introduced we know have definitive proof of a weapon capable of liberating entire Borg cubes all at once if they are disabled. And what happens? We use it in ONE mission. We also see definitive proof that the Borg are not mindless automatons with all of their personality wiped, if they were assimilated long ago, as we personally witness the returning of a former Borg drone to his brother. In other words the Borg drones are still people who are unconscious and stuck in a body controlled by the Borg and we have a super easy and very efficient way of returning them to their former selves. And after all this is done we go back to Defera and continue maiming the assimilated populace, with the reason literally being nothing more than "they were unconscious anyway so might as well kill them".
Admittedly, the weapon is indicated to be something of a one-of-a-kind thing that is hard to replicate, seeing as the Cooperative lends it to you for that one mission so you can help them with that part, and then asks for it back when the mission is done.
Though it is possible to summon science officers when using Medkits.
The Klingon Empire is experiencing a massive renaissance, having conquered the Gorn, the Orions and the Nausicaans, and integrating their species into the Empire. Now, this mainly has the benefit of allowing KDF players more variety in available races. But it also has the side-effect of giving the Klingon Empire a massive cultural shift. Where once the Empire was chauvinistic against all non-Klingons, only admitting ethnic Klingons into the military and government, STO's Empire now accepts Gorn, Nausicaans and Orions to captain ships, and even integrates the ships of those "subject" races into the KDF fleet. And when playing as one of those non-Klingon KDF characters, you will occasionally get the same dialogue options as a "true" Klingon would get. While this could be an example of Gameplay and Story Segregation, it might also be that the Klingon Empire is slowly integrating those cultures into it's own, to the point that now Klingons see Gorn, Nausicaans, Orions and the other various species within the Empire as complete equals. This means the Klingon Empire have learned something from the Federation: from diversity comes strength.
Koren note The Bortasqu's Captain. often makes comments that jeeringly ask if someone is afraid, or that this situation wouldn't be so terrible if someone hadn't done this in the first place, making her look like a Spoiled Brat... however, it may be deeper than that: Klingons regard honor above else, and many absolutely despise cowardice, treachery, and so forth.
Her asking if someone is afraid could be seen as irksome to her, though possibly she's a minor Horrible Judge of Character (Worf: "Koren, prudence is not cowardice."). Then there's the bigger events, in which Tiark Jirok initially claims the Jenolan Dyson Sphere for the Romulan Republic - which could be seen as a betrayal by their so-called allies; and when only two ships show up initially in the defense of Qo'nos, which could look like their allies abandoned them - not just a jumping-to-conclusions a Horrible Judge of Character might do, but a (vocal) outcry against another seeming act of treachery.