> I’m still surprised why Fi has not been dropped

It is probably something they already had internally that they figured they could monetize easily. They develop Android and RCS. Operating their own MVNO could very well allow them to simplify some things.

> many customer support issues.

Huh? I've used them for years. Never had issues which were not directly related to T-Mobile's network. There were no issues the few times I interacted with support.