It's not collusion, it's a natural consequence of the way healthcare billing is structured in the US. You don't get to comparison shop but also have a captive audience (you're not just going to decide to be blind right?) so there's no pressure to keep prices reasonable.

This makes a lot of money for powerfully connected companies, so don't expect it to change anytime soon. This is why our congress and mass media treat Medicare For All as a joke or something to attack politicians on even though it's popular with a majority of Americans.