The point is there isn't actually competition on the streaming services: there's competition between the media companies on the production of content, who then restrict the availability of said content to a subset of services. Instead of the situation with music where it's normal that an album is at the very least available on the big 3, if not many others. And there's generally not a shell game where things start and stop being available as well. An actually competitive market would separate the streaming services from the content production and the incentive would be for the content to be available on as many platforms as possible and the platforms would compete on quality and features instead of how much of a catalog they can license this month.

(similarly with steam: the blowback on epic was due to exclusive games, not the mere existence of it. Steam-exclusive games are also a problem, but generally one which comes naturally from its market position and not artificially through contracts)