I think you don't understand individuals. We just want to eat - Individual developers really only care about making money.

If a fart app is going to make an individual developer good money, nothing you can say will stop them from being made.

If developers can seemingly make more money by charging less, nothing you can say will make them stop charging less.

Microsoft set a price floor to attract developers who aren't thinking about 1 year in the future, when Microsoft will either remove that floor because their platform is successful enough (they don't have to court developers), or they will kill the platform itself (and your app).