I can only speak for myself, but writing the PC is really hard and not very enjoyable. Mostly because of all the variations that needs to be taken into account.
The drive for me when writing is the NPC, since that character is my own creation and I can mold them however I want after what kind of kink I'm going for. I can use whatever personality I want and I can do things like character growth and stuff like that.
When you write the PC you can't do that. You need to take into account that the PC is very nebulous. The PC can be a man, women or herm with 3 different personalities and a billion different body parts. If you are a hobby writer like me, you just avoid most of that stuff because I'm doing this for fun. The only variation I kinda enjoy to do is Champion/Dark knight/Bimbo variations. And some quick blurbs about penis and cum size.
It's also a reason I avoid writing anything with Etheryn. She has 3 major variables resulting in 9 combinations you need to account for if you want to include her in your scene.
TL;DR: the NPCs being "super-special snowflakes" is because they are the most fun to write.
Allow me to preface this by saying. I'm not specifically coming at you. I pay zero attention to individual writers, outside of those brought up here. And the ones who pop up the most in game. So I have no idea which finger in the pie you are. For all I know, anyone you've written is off to the side just chillin.
But this is what I was talking about. How it's like people are living vicariously through NPCs... because they are. We are shadowboxing/competing with other people through their OCs. Writing for themselves and their enjoyment. Which isn't necessarily an issue. But it does happen even at a detriment to player experience. Again not you specifically, but it's like some folks forget they're making a game for others.
But you know what? It's also on me. Expecting corporate level checks and balances. From a Patreon game that's essentially a bunch of short stories glued together. Then single stapled to the game itself. That's my fault.
Like you got normal games out here where you're side eyeing and asking if something's a self insert.
Then you got CoC2 over here like.