Actually, Apple doesn't have the right to set it's rules and decide who can and can't be on their platform. Monopolies lose that, and Tim Cook was grilled on this exact topic by the House Antitrust Committee just days ago.
Which is to say, even if the current laws allow Apple to act here, if it does, the next laws might prohibit it from doing so.
It's not a monopoly, there is NO definition that fits for Apple being a monopoly. DOn't like Apple buy an Android. Android is more popular and has the same rules. Game Developer? Don't like Apple's rules develop for Android or Switch or PS4 or the Web or PC etc.... Apple sells a platform and it's successful but it's absolutely not the only platform around or even the biggest except in sales. Tim Cook wasn't grilled in good faith, he was grilled for political gain.
Which is to say, even if the current laws allow Apple to act here, if it does, the next laws might prohibit it from doing so.