None of those are big enough barriers to entry to keep even the small players away, meanwhile the big dogs are starting to show a lot of interest in streaming music (admittedly for music you "own" at the moment, but it would surprise noone if this were to change overnight).
Apple has the marketing weight and a history of solving music licensing issues, Google has a track record of throwing money at problems to solve them, and Amazon is just about to make a major hardware play.
Spotify's only real hope was to latch onto the latest big thing (conveniently an infrastructure provider, so unlikely to launch a direct competitor) and hope to ride to success on someone else's coat-tails.
I have no idea what the contracts between the two companies look like, but I would have to imagine that they are heavily in Facebook's favour. After all, it would be a lot easier for Facebook to replace Spotify with another provider than it would be for Spotify to replace Facebook.