E.g. cloud providers must provide cheaper and cheaper service to stay competitive with other cloud providers. This in turn drives down costs for all technology in society.
Sure a union could try to take that profit and feed it into wages instead, but that's worse for society in the end.
When profit margins maintain at excessive levels it's typically an indication that there's either a first mover advantage, or the company is a pseudo-monopoly.
I'd argue there are some big cases where that applies today