It's the fact that church comes with an actual presupposition that it isn't optional, while de facto being optional.

Going to church (in contexts where denomination shopping isn't a thing at least) means going to a place where a person is not there to validate your particular perspective but instead often to tell you and everyone else in the group to do better, publicly, not because they're better but because they appeal to higher principles whose correctness is taken for granted buly the congregation.

See also: the absolute brain lottery winners on the internet bitching that the pope isn't a real catholic for telling them they're bad catholics (arguably bad christians in general, definitely bad people) for dehumanising poor people and immigrants legal and illegal.

I'm far from a catholic (that is, I'm actually a lapsed catholic if you ask the church, but I was never a believer, just born into it) but there just isn't a space where you're going to participate, respect the ethics and morals, still fall short of them, be chastised, and be forgiven, that doesn't involve some religious aspect.

I do think there's a special thing about church that is this bigger than yourself experience

I'm pretty sure that's only the case if you're a believer. And, in general, people who aren't believers don't go to church, so you're selecting for a group of people who want to believe in something bigger than themselves.

That's not a car