1. How big is the pie?
2. Who gets what share of it?
Here in this thread, almost everyone is saying that the total pie for music isn't that big compared to the number of people making it today. As production costs get lower and lower, more and more people can be become musicians and that pie gets sliced into smaller and smaller pieces. Meanwhile, there are only so many hours in the day one can listen to music, so demand is relatively fixed. I agree with others that this is maybe unfortunate, but is basically just reality. Just like writing and working in zoos, occupations that have massive intrinsic reward are rarely compensated well financially.
But there's an entirely separate question. Given some pie of whatever size, are companies like Spotify getting a fair share of it relative to musicians? It's sad if musicians can't make a living can't make a living off their music. But theatre actors and poets rarely do either. But it seems wrong that at the exact same time, businesses are raking in billions of dollars off that exact same music.
We aren't outraged that poets are underpaid because there simply is no money there. There isn't much money to go around in music, but even so, the distributors are taking almost all of it and leaving little for the actual musicians.