re: My google play music seems to play the same 80 songs on shuffle.

It's probably too much work to look into... but I wonder if the songs that are more commonly repeated tend to be owned by the same company.

Like, maybe Google has a more favorable contract with Universal Music Group than it does with Sony or whoever else. If so, part of Google's algorithm might be to favor the artists under that licensing agreement where they may pay less in royalties. I have no idea if the royalties are different or the same for the large music groups, but if they are different, it would be unlikely that Google, Spotify, etc. wouldn't push music for which they had to shell out less themselves, allowing them to keep more of your $10/month.

Just a thought.