Well, that's not entirely true, Apple can't exactly do what it wants. As other comments point out regarding Microsoft, Microsoft were forced to allow IE to be debundled and other competing browsers installed, because having a monopoly on a platform and using that platform to enforce anti-competitive practices is illegal under anti-trust law.

So given Apple's marketshare (not a monopoly per se though pretty substantial), and given they both control the platform that people pay money to access, and promote preferential treatment of a first party service at the expense of any third party services, it sounds pretty ripe for an anti-trust lawsuit.

The same I believe has recently been applied to Google in the EU for using its monopoly to promote its own product search results above other online stores.

The only difference now is, the teeth of anti-trust regulators are a lot more dull than they were in the 90s, for various reasons.