You are advocating for centralization in the end with a service provider for fediverse instances. And not everyone has a domain or knows how to get one.
I'm fine with pleroma and it's ability to federate. I made some changes to soapbox, since it was the cleanest interface but lacking in some departments.

The app was used to say how simple the process would have to be for the masses to adopt it. We can not expect everyone to know how to setup a server/maintain it.