True, but these are generally limited agreements among a few individuals (at most a small handful at the top). Pulling off a big conspiracy between many powerful competing actors carries too much risk of defection. It may be possible but it’s certainly rare.

I do think that these limited agreements may be copied by other people in similar contexts, for instance there were other tech firms who made similar agreements with their own competitors. And the big tech anti-poaching agreements may have themselves been copied from similar agreements made in other industries, such as finance and fast food. The illegal conduct probably spread organically through word of mouth, as execs and board members informally exchange this sort of “best practice” with each other.

It’s likely that big shareholders or board members could hold private meetings to advise the CEOs of their companies on how to pull off this sort of trick, if they think it would help the stock price. Given how many people sit on multiple boards, this could be seen as a sort of conspiracy. It’s still very informal and of course it’s nearly impossible to prove.