Apple is not a monopoly. Any competitor can compete with them on price / fees and win if Apple really does not provide enough value to people to justify their prices. I genuinely hope that it happens. I just don't agree with the common heuristic of "hey you have a good thing going there, you shouldn't be allowed to have anything that good!"
Why is Apple not taking 99% of the revenue and takes 30%? Because if they took 99% nobody would develop for their platform. So there is a sweet spot between 99% and 0% where the services and market they provide is good enough that the fee is worth it. Currently it works for everyone as Apple's and developers' business is still booming after all those years. Developers want more, Apple also wants more, everyone wants more, all is natural. Wanting to optimize your gains is natural for everyone. It is not illegal, and should not be.