That would be awesome. Right now, you usually get an even less favorable choice than that! For example with Spotify, you either use their app and see ads, or you pay and don't see ads, but still are forced to use their app.
That is probably a licensing requirement for the providers of the music. They likely require some form of DRM in their agreement with Spotify.
If anyone could make an App, how would Spotify be able to properly track song plays and whatever else they need in order to pay the rights holders?
Plus, someone would end up creating a 3rd party client that silently plays some song, unbeknownst to the user, in order to rack up plays and earn more money.
