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.