Spotify puzzles me. How can it be sustainable? For my listening purposes, the free version is more than adequate. I don't mind listening to a new album with two

Spotify puzzles me. How can it be sustainable? For my listening purposes, the free version is more than adequate. I don't mind listening to a new album with two or three interruptions for adverts (just turn the volume down), and I don't mind needing to be near a computer to hear the music (I have good comp speakers). I subscribed to the service for a while but didn't renew it because I'm happy with the free service. Post-Spotify, the only reason for me to spend money on the music industry is to 'support' their efforts. Previously I would happily pay for an album if that was the only legal option. And even if you do subscribe - £10 per month? I think anyone who loves music enough to really take advantage of the service could justify spending £40-£100 per month. I don't get it. I'd like to see their revenues. And the opportunity costs. I have three theories 1)They plan to wean the public off any/all illegal filesharing by offering a far superior service for next to nothing. Then, when the public has sufficiently 'de-skilled' from piracy, they will start raising prices without losing customers. 2) They've decided the battle against piracy is futile and they're settling for a tragically reduced ROI over potentially nothing at all. 3) It's a massive blunder.