Earlier quoted context omitted.
when you follow somebody, you put their public url in a list, then when you open the app it requests the photos from everybody on the list? I see no reason why everybody could not run a web server on their phone.
So if I follow 1000 people, I make 1000 requests every time I open the app or refresh my feed? Also not everyone can be on a stable connection with a public IP address with good upload speeds 7/24. In the ideal world: sure. In the real world: impossible (at least for any foreseeable near future).
It's not perfect, but if we want self hosted, we have to start somewhere and start working out the problems.