Well, it is definitely in Spotify's interest to keep as many quality artists as possible on Spotify, and that probably involves paying them.
/s
If selling CDs through a store could earn you (using simple but realistic numbers here) $100k per year, and Spotify streams to the same audience size earn $1k per year, it’s not unreasonable to expect that Spotify should add a hell of a lot more value on its end, perhaps in the form of driving listeners to artists — especially if Spotify possesses the means to.