I don't know. Music streaming services do pretty much follow this separation of content and service. At least unless you really care about exactly which music you can access which I think most people don't.
(That's probably partly why music streaming services don't compete on content; most people don't care exactly which funky music they're listening to as long as it is funky, and had most of the popular stuff. But they definitely care if they want to watch Stranger Things and they can't watch Stranger Things but maybe you're interested in these other crap knock-offs?)
Anyway the point is music streaming services still find ways to compete. I guess they would prefer it if they could compete on content though.
Some recommendations and playlists I guess. Most of us (outside of Spotify) get them because of a bundle with other offerings from a vendor. Spotify definitely has a following but I don't really care much and have an Apple bundle anyway.
Idk. I can imagine an alternate universe where Taylor Swift's new album was exclusive to Spotify. All the Swifties using Apple Music probably aren't interested in "Taylor Swift knockoffs".
It's not entirely obvious to me why this hasn't happened.
That said, my interpretation is that bands don’t really make a lot of money from streaming, it’s more of a promotional platform for them so it makes sense to just be everywhere to be seen. This is not true for tv/films.
If your song is streamed 10 million times chances are a festival will call your manager. The money is in concerts not albums.