Some things do charge different amounts though. YouTube Premium for example is more expensive if you subscribe in iOS but maybe that’s just because it’s Google.
They also could have just not let anyone subscribe through the iOS app. Lots of things do that.
Because that’s where all contributors are.
Personally I’ve been moving towards dual hosting everything on GitHub + Codeberg. It’s pretty easy to setup CI to keep them in sync, and I’m open to dealing with the annoyances of managing multiple issue trackers.