The ugly truth is that most people (I dare to say 99%+) don't care much about music. They just need to listen to something while doing their jobs.
Which is why you'll never see me get off the comfy "local only" train, buying CDs and sailing the high seas with my skull & crossbones flag if needed.
There were ads, but as you mention, people don't seem to care much.
The quality check was the non personalized streams cathered to please its audience and competition among stations. So, the solution is to kill targeted algorithms and monopolies, ha.