Spotify pays them more than radio, per listener, and significantly more than YouTube does per viewer.
Indeed, the music industry must be the only industry where you give away more than your product to sell your main product. The pop promo or music video contains the soundtrack plus some expensive visuals, but the soundtrack has no visuals. But musicians do not seem to see this as contradictory.
The music industry is following the lead of the TV industry in needing active management of distribution across release windows, platforms and territories.
But this is more of an art than a skill and the result can mean millions of pounds lost or gained, or even whole careers.