Where does music come from that streams?

Is this a question about sourcing of the particular master or the way that streaming is licensed? Traditionally, the label (master side) did the deals and cleared the publishing rights (standard, compulsory rates on the publishing side). The Music Modernization Act paved the way for simplified licensing but that has nothing to do with source material, per se. 

I've had a Qobuz license just to experiment with-- the biggest shortcoming to me was that the repertoire was largely popular stuff, but not "deep"--and having some familiarity with different masterings of the same track, or different recordings of it, I found the catalog to be rather shallow in the area of post-bop jazz. Granted, a lot of stuff is on some of the better platforms and may satisfy the needs of a lot of listeners. But for me, streaming hasn't scratched my itch for "deep catalog" stuff. I also wonder to what extent some of the higher rez stuff is simply uprezzed. 

I get why people like streaming. And see the value in it for a lot of users. It's just not what I'm after. 

@tomcy6 -right on, but to expand on that, the record label may own the master but often doesn't not have rights in the musical composition. Those rights, a/k/a "publishing" side, also have to be cleared but there is a compulsory license for that in the US. 

Although folks aren't interested in the mechanical aspects (indeed, in publishing, the right to record a song was called a "mechanical right" for reasons having to do with the history of audio), it's important to recognize the distinction if you are at all interested in how the industry works.