Then what is empirically wrong with trio programming? If the pair programming wonks actually have data to show that it is a net benefit, then they surely must have evidence showing that 2 is a good maximum on return.

Like to this day, I have never seen any reproducible strong evidence provided that pair programming is beneficial. And I don't know if I would call the occasional ad-hoc (unstructured) "pairing" anything other than what a normal person would call it: "two people collaborating like normal fucking human beings."

But if there is evidence that 2 is better than 1, why is 3 or 4 not even better?

Have you personally tried it? It's great!

So call it collaborative programming. People tend to work well with someone checking their work, and more than two is limited by human communication. You're creating a strawman that I'm saying "The more, the merrier". I'm not.