I'm not a lawyer or legal expert but my layman's understanding is the laws on antitrust are a 100 years old. Most of these companies skirt them "technically". There is thing about proving consumer harm and some of these, in the short term, are arguable better for consumers. Likewise proving an actual monopoly with old time definitions is hard because in a lot of cases there is technically competition.

Let me end by saying, I think it's horse she and they are plenty anti competitive practices out there, but the FTC is fighting with a hand tied behind their back with the laws in place.