Obviously not. Which is why we have antitrust laws. If it was in the self-interest of the most succesful capitalists, we wouldn't have to have laws about it.
> I don't think anyone disagrees that monopolies and other anticompetitive behaviour is a thing that exists.
There are people who never learned this or have essentially forgotten it. Some ideologies bury such truths.
Among business/tech circles, there is a fairly common disdain of regulation. People can conveniently forget that self-interest taken too far can destroy the conditions that make competition work.
It is one thing to criticize a powerful monopoly that isn’t you. It is another thing to say “Oh. Maybe what I’m doing is part of the problem.”