There are plenty of music streaming services at the same level of quality and within the ballpark of paid subscriber base as Spotify. It wouldn’t qualify as a monopoly.

Music streaming isn’t the kind of good that falls under common carrier so I don’t think the analogy of the electric company fits. People can easily go through life not subscribed to one. I for one only have iTunes Match which isn’t the all-you-can-eat style of Spotify/Apple Music/Play Music/Amazon Music/Tidal/etc.