Specifically about Kingmaker, I am personally also rather annoyed about the amount of whining on display.
However, let me play devil's advocate for a second. I think we shouldn't ignore the reality here. The barrier to entry for Kingmaker isn't very low. Pathfinder can be a pretty daunting system, and while the game does grant you enough info on specific details, it's easy to get lost if you don't have a solid grasp of the basics of the system (which the game doesn't provide). So should players start by reading the core rulebooks first? That hardly seems like a good idea. There are many CRPGs where you start out, learn as you go, and wing it. But Kingmaker does require some strong insight into the game from the very first screen of character creation. It's very easy to create completely inept characters if you're not familiar with the basics. When I played Baldur's Gate for the first time, I just took that lovely manual that shipped with the game, read it diagonally, and I sort of understood the basic of BioWare's implementation of AD&D. But games don't ship with solid manuals anymore.
You can see a lot of people referring to Nerd Commando's videos (is he the same guy as Pope Amole btw?), but sitting through some of his videos can be a bit... challenging as well, and I can totally understand that people would rather start playing the game instead of watching random Youtube videos first.
I think the complaint about the swarm enemies is rather legit actually. Personally, I wasn't familiar with how swarms worked in Pathfinder, and this had me rather confused as well. Mind you, I wasn't angry or anything (hell, this is probably the smallest and least interesting "quest" in the entire game and completely optional), but it does beg the question: how is the player supposed to know how to beat these enemies? One could certainly make the case that the game simply doesn't provide you with enough information to overcome this "challenge".
Another complaint you see often is that in the first few hours it's not entirely clear how recovery, resting and camping work. I agree, it took me a few seconds to sort that out as well (the resting screen is a bit confusing the first time it opens). A very short hint, popup or in-universe explanation could have gone a long way in explaining to people how to get rid of certain stat penalties etc.
TL;DR: Yes people complain WAY too much on the various forums, but I think it IS true that we can do a better job at teaching people how the RPG systems work. Personally, I am absolutely not against accessibility as long as it doesn't compromise the actual gameplay (by streamlining etc.).