If there is some kind of collusion, then that is a clear and provable anti-trust violation, and anyone at any of these companies can make a lot of money being a whistleblower.

Yet somehow no whistleblower ever seems to show up. No proof is ever offered.

And for the oligopoly idea to work, you feel full cooperation between everyone. As soon as one company doesn't play along the whole thing falls apart.

Since there are indeed no shortage of long-lasting choices, that leads me to think this isn't really a problem.