Why do I have to say "FM-Radio ein" and not short "Radio ein"?

Second. Why do I have to say "FM-Radio ein" and "FM-Radio aus" ("ein" <-> "aus"), but "Musik an" and "Musik stop" ("an" <-> "stop")?

But it doesn't really matter, because the voice control doesn't work anyway. *lol*

But because this reason I would prefer a response beep like google assistant. ("hey, sena" <beep> "do something")