There is a story from the early days of Napster where music industry executives discovered the service.

One of the executives describes it as:

"We had a laptop open and we tried to play 'stump the Napster' but not matter which obscure song someone threw out, it was there!"

To put it in modern terms Napster indexed:

- every song

- on every user's computer

- and then indexed all of those songs on a central server

I suspect people would pay for a service that offered this (same for movies) but a combination of licensing, IP protection etc don't allow that to happen.