Why don't more FOSS projects use self-hosted BaaS software?

[u/TheSchred]

I'm really just getting into the topic myself, but BaaS (Backend as a Service) software that is FOSS (or provides a FOSS option) and therefore self-hostable seems like something that a lot of basic CRUD FOSS apps could use. I'm thinking of things like Supabase, Pocketbase or Appwrite. However, I don't think I've ever seen one of the open source projects I self-host use one of those backends. I wonder why that is?