I think the big reasons for most people boil down to one or both of two things:
A) People having 0 trust in Google. I.E. people do not believe that paying for their services will exempt them from being exploited, so what’s the point?
B) YouTube’s treatment of its content creators. Which are what people actually come to YouTube for. Advertisers and copyright holders (and copyright trolls) get first-class treatment, while the majority of content creators get little to no support for anything.
I’m also neither a mod nor member. I have never posted nor commented in c/vegan. I do not habitually downvote posts from c/vegan. I am banned from c/vegan, as of about a week ago.
If that isn’t overreach, I dunno what is.
If they don’t want non-members to be able to vote or comment on their stuff, that’s fine, take the community private.