You nailed it. Music has a fundamentally different mode of consumption from music. People consume music in so many different ways and contexts. Music doesn't always demand your attention like a sensory-engrossing medium (like movies). But when music demands your attention (like having to change providers to hear a specific song) it introduces friction that is unnatural to that medium.
Spotify has a lot of competitors biting at it's heels, they're certainly the largest (and IMHO, best) at what they do, but they've by no means locked up the market.
They're not exactly at the mercy of the labels, but they probably can't afford to piss them off either.
This could lead to cartel-like behavior among the stakeholder labels and crowd out the smaller players, but that's basically been happening in the industry for a long time so I'm not sure how big the impact would be.
If they start poaching artists from the labels who own the back catalog or if the labels start to see Spotify as a competitor instead of customer there will a reckoning when it comes time for Spotify to renegotiate their licensing terms with the labels.
And then of course there's the risk of becoming a record label. For every Bruno Mars that blows up there are 30 or 40 other artist that failed to break. And each of those flops costs money and requires resources such marketing, A&R people etc.
>"All they need to do is to get people to stream less licensed content and more own-produced"
People want to listen to what they want to listen to when they want to listen to it. That's the whole value proposition of streaming for users. If someone has a specific record or song in my mind you aren't just going to persuade them to try some "non-licensed" content instead. It's not a sports drink.
>"I would assume that Spotify's music licenses are highly variable cost, ie almost entirely pay-per-stream."
No its most certainly not pay as you go. In fact the labels demand a certain percentage up front.
Netflix has plenty of third-party content.
However, in my experience in the UK, if you pick a well known film at random and look it up on Netflix, there's only about a 5% chance they'll have it.
Not the sort of library that will have users throwing away their personal collections.