Maybe because we all know what the word "tax" means?
In this case uber goes above state and the fee they are charging is actually a tax. Calling it a fee doesn't change nothing.
They are also not very original, which could justify a bit their high charges. In Europe websites and apps for car sharing existed for decade, most of them were for free, but a lot of them had to quit due to the laws. Uber has enough capital to fight on the highest level and ignore them..
I guess Argentina should copy their app and use it under their regulation. I wonder how uber would react, when someone would breach their rights?