Earlier quoted context omitted.
It's not an "undeniable right" but it's also not like there are a lot of other options. You can say "just move to another platform" or "then make your own platform" but you also have to be a realist. This is why antitrust laws exist - sometimes the market realities make this nearly impossible.
But where is the line of lots of options vs not a lot of options? iOS isn't even the most popular mobile operating system.
Also for some serivces iOs users are the large majority, like more or less any "real premium" service (Like apps you have to pay 10 or so+$ a month or 100+$ when buying them).