The question is would Spotify make money subscription revenue at $50 a month than $12. If the volume of subscribers at $12 is such to generate higher total subscription revenue then it makes sense to keep it low.

I think your point is pretty valid though, if I listen to 6 hours a day I am contributing way more towards band payouts than someone who listens to a few songs a day, even though I am putting in the same amount. The direct connection could actually encourage people to subscribe, have a page showing your contributions to each band you listen to.