Unless you're a really big artist with a favorable contract, you get paid shit for selling music, be either through streaming or direct sales (physical or digital). That's if the artist even managed to fully repay the upfront they got to record the album in the first place - because until you've repaid that, all of the money goes straight to the label.
For soundtrack composers it's even worse, as it's mostly done as contract work and they very seldom get any royalties on sales. Soundtrack music has very little commercial value other than its original and for advertising/marketing purposes. That's why, for the soundtracks I've composed, I've structured my contract so I retain the rights to freely distribute music with a CC license - as an artist, I'd rather have people listening and enjoying my music, even if I don't make an extra cent from it.