I am not saying nor implying that what the Big 4-5 are doing is illegal. I'm merely noting that these companies have an outsized influence and the ability to force the markets to behave in specific ways, not all of which are beneficial to society.
There doesn't have to be a law, for an individual or organisation, to notice and opine that these companies DO have an impact which would be very hard to achieve in free and fair markets. Law usually follows disruptive innovation and capitalism and capitalists generally try to run circles around policy making.