Because there's a fuckload of people streaming and because they've already paid for it, they do it for hours every day.

There's artists on tens of billions of streams. That's enough to live on for anyone.

Of course if you've got only a few thousand streams then you're going to make fuck all, but you probably weren't going to make anything anyway. You might get a few fans from discovering things on Spotify who might turn up to your gigs or buy that T-shirt or whatever, but with that number of listeners you probably wouldn't even have got any radio play in the old days, let alone make money from albums.

Most people never make money on art, no matter which art it is, or what business model they use. It's just life. If you never hit that mainstream vein, you're going to need a proper job.