i don't imagine many people in off-topic are even particularly that engaged with the game or its fandom to that deeply an extent, so finding answers here will maybe be a bit difficult
i also don't imagine the constituent fanbase is necessarily all made of "stuck-up asshole(s)", but... it seems plausibly representative of at least a lot of people maybe. i think i moreso wonder why you think that, what it was you observed and what you associated their responses/reactions/behaviors with (or rather, maybe what you were reminded of? or what you recognized as familiar enough from it to make the connection?)
for my own thoughts, it's a bit complicated for me to describe my impressions, because they are not-at-all clear, nor are they really sourced by anything i can prove or justify all that well. they're all just my appeals to sympathy and intuition and whatever else. the omori fandom isn't really totally made up of children obviously but it is very very deeply associated with them in my view, and i wonder if it resembles or represents some behavioral or cultural or narrative similarities between the kinds of populations that enjoy this game and the relationships between the narratives of the game itself and those of other games it stands shoulder-to-shoulder with. and in my mind, i associate the omori fandom with some thick whispering afterimages of the undertale and deltarune fandoms, although the texture and flavor is much more distinctly specific than just being a game with mere similarites to those two
...in fact, i haven't played it either, and i don't encounter or observe the fandom/community very often or actively at a personal level these days, but i was familiar with some of its meme culture and some of its emergent creative impulses, as seen through the many many many many fanart pieces and animations and song remixes or songs that adopt the qualities of the omori ost... it seems very very close, and there are different varying elements of the undertale and omori fandoms' histories (of which i don't remotely know by heart, i say these things with the wavering confidence of a person trying to half-remember the details of what they read from a face the other day without prescribed glasses) which make me think of "highly-and-quickly opinionated" or "defensively idealistic" or something along those lines
that kind of flavor/texture reads through the specific kind of emotive tastes these games give off, in a way that can readily create a fever dream of catharsis for 13 y/o artists and animators and whoever else, and just... that general pursuit of catharsis and sensation tends to be what i imagine could characterize the bulk of why these fandoms are enabled to enjoy it the way they do
and it seems to carry across a lot of internet fandoms, honestly, but it definitely is how i could feel about omori or some other places... i don't know if any of this was an answer so much as a vague nod of possible understanding of the impressions you've had and questions you've carried
at the same time, i really really do not like characterizing people this way. and often times i maybe sympathize a lot with a great deal of what i anecdotally observe from people when they're reactive or opinionated or snarky or otherwise interpretably unpleasant for anyone that isn't already inside the circle of interest
i, in fact, really adored the emotional/sentimental aspects of these games. i was very very into undertale when i was a teen, and i did encounter omori with some level of interest that kept me wandering the community's fanmade content for some satisfying representations of certain experiences. i don't know if any of these impressions and personal experiences ever necessarily mean something in particular... but i do wonder about it...
i wish i knew more, understood more, and i wish i could see more about what led people to find what they did and engage with it in the ways that they do. i wonder what people's lives are like, and if any of it has any bearing on how they think of these games, if they were affected by something that drew them into these games
so much to wonder about...
also desperately wishing someone has some clearer sense of what might reflect whatever it is that causes the behaviors we interpret and believe are representative of people here
