You don't need to use one of these apps. PieFed is perfectly capable of running in a browser, even a mobile browser. Also, you can install PieFed on your phone as a PWA (progressive web application) so that it can be run on your phone exactly like an app.

Some people prefer a different interface though, so these other apps provide options for them. Also, some people are making a transition from lemmy and these apps generally also support lemmy, so it makes the transition easier when the interface stays the same through the transition.

It’s just the app…. you need to use an app to interact with almost all services these days. Maybe you are referring to having choice to be unintuitive? Sure it’s more work and you have to think about what fits most your needs but i think it’s a net benefit to be even have to choice.