In terms of mass-market success, goodness of recommendations is like, #12 on the list of must-have features for a (streaming) music service.
#1 is "It must have all of the music", which is really a lawyer problem, not an engineering problem.
(#2-#11 are just variations of "No no, I mean all the music", "Does it have really old music, like X?" "What about really niche music like Y?" "Oh, oh, what about Z? I bet it doesn't have Z.")