MS was anything but lol, they had a swarm of lawsuit dramas over by then. Only Apple glazed MS because they quite literally saved them from bankruptcy which they only did as insurance against a proper antitrust case.

Google was newer but they also weren't a private company, they were riding silicon valley money to the moon.

Regardless, Steam is a monopoly but their immediate competitors are the only ones chucking anti competitve measures around like crappy DRM and price lockins.