Buying a generic service and closing it down in a way that it's inaccessible outside of their walled garden sure sounds anticompetitive to me.

Then you are correct in your original comment: that isn’t “acting like a monopoly”. There might be a different term for it, but “monopoly” ain’t it.

Apple is one of the most dominant tech firms in the world, leveraging their wealth to buy companies and then shut out their competitors from the service is pretty much the quintessential example of an anti-compettive behavior, especially because of the very clear consumer harm produced by shutting out all those existing users. Having a monopoly is not illegal and not the issue, anti-competitive behavior resulting in clear consumer harm is.

You can play your word games, but this is how the FTC describes [1] it.

> Judging the conduct of an alleged monopolist requires an in-depth analysis of the market and the means used to achieve or maintain the monopoly. Obtaining a monopoly by superior products, innovation, or business acumen is legal; however, the same result achieved by exclusionary or predatory acts may raise antitrust concerns.

https://www.ftc.gov/tips-advice/competition-guidance/guide-a...