But two wrongs don't make a right. Yes, they take advantage of their position in pricing and yes, they have benefited a lot from offering their infrastructure for free. But that does not make it okay to use the infrastructure they provide for your personal gain just because they are "bad".
We also need to differentiate between Google and Apple here, as the case is totally different. Google simply has a large market share on Android; iOS, on the other hand, has (nearly) no option of alternate stores and the App Store is not free. That's why I mostly talk about Google here; with Apple, it's an entirely different story.