Why have we normalized "app stores" that build software whose authors likely already provide packages of?

I've been using Obtainium more recently, and the idea is simple: a friendly UI that pulls packages directly from the original source. If I already trust the authors with the source code, then I'm inclined to trust them to provide safe binaries for me to use. Involving a middleman is just asking for trouble.

App stores should only be distributors of binaries uploaded and signed by the original authors. When they're also maintainers, it not only significantly increases their operational burden, but requires an additional layer of trust from users.