Really interesting, odd move imo. As others have said, this is a highly diverse industry, with entrenched players and smaller players as well. I think it's interesting to consider 'why'? Clearly Bezos thinks he can make money at it. A lot of money I'd wager.
In US law, the key phrase from Northern Securities Co. v. United States, 193 U.S. 197 (1904, "the first railway monopoly case") was "in restraint of interstate commerce."
The trust was deemed by the Supreme Court to have been created for the purpose of ceasing active competition between the companies who joined it (there having been recent strife between them in the news, the trust being the negotiated solution, to back this purpose up).
So, very different. A similar case would be if AWS, Azure, and GCP decided to create a holding company that combined all their assets.
