> I think the point of a lot of configuration formats is that they don't want their configuration to also be a full-fledged programming language.

That seems to be everyone's initial goal, but then it inevitably gets leaky.

I think the dominant split here that forces everything into a weird mismash is that nobody really wants to have to understand arbitrary programming language configs for third-party stuff, they want to read config and know what's going on. BUT for their own stuff, they find reasons to want more power and expressibility...