Not that this excuses Spotify, but artists got the short end of the stick in the traditional system too.
Artists don't get a 10% cut each time a song is played on Spotify. The only people getting rich with Spotify is Spotify and the label that grants the content rights. The artists do get almost nothing.
- if artists demand too much payment from labels, labels won't sign them
- if labels demand too much from spotify, spotify won't sign them
- if spotify doesn't sign enough labels or pays too much to them, it will die either due to not enough music or not enough revenue to find growth.