This is how all businesses work. If there was no way to make profit then businesses would not exist. Apple spent billions of dollars creating an app platform with a clear monetization model that did not get in the way of them accumulating a lot of valuable apps and users. Developers are not forced to make apps for the platform nor are users forced to use the app platform. Other app platforms can impose lower fees and developers are free to release exclusively on those platforms if they wish. Apple hopes that the developers willing to tolerate the 15/30% fee for what the developer gets in return will be good enough to make their app platform competitive to users compared to others.
It's not just defending a trillion dollar company, it is defending the right to set your own prices.