I find it's not just the classical people, in fact I don't get much it from them, just a bit of snobbery from young ones who are fresh out the conservatoire. For example, several times I've tried to talk to young classical people about music and get snubbed, but the exact same thing happened with jazz musicians (I am literally a jazz musician too, it's not fair haha!)

Once people know enough about music theory (i.e. they are not a student of it any more) I find they become really open minded because they understand the theory is just that. They also tend to have an appreciation of the range and depth of music across the globe. I think this "classical theorist as snob" thing is a canard, a cultural meme like a snooty character in a film. All the composers I've met have been incredibly open minded.

The closed mindedness is all over the shop. I spoke to punk rocker recently for whom all music that isn't their taste is just "shit". The snobbery is about defining borders of "good" and "bad" and differentiating poeple and groups (me = cool/sophisticated, you = troglodyte). If you look at r/wearethemusicmakers it's a grim place, reminds me of school where everyone just took the piss out of you for doing somehting wrong or not being cool. On the synthesiers forum they downvote people for posting their nice musical efforts, and if you have the wrong gear you get downvoted. It's about status for some; meanness to outsiders and identity policing.