If you ever studied Tax Law, you would understand that, once a government approves additional taxation, it will almost never accept to relinquish it. Furthermore, Brazil is a federative republic - the President is not able to change the whole taxation system at will...exactly the same happens with the horrid tax system in the US - the only advantage is that taxes are still lower over there.
As for corruption, please stop this usual mongrel dog complex that affects many Brazilians - according to the latest Transparency International reports, Brazil's corruption levels are way better than China and Russia, better than most of the Americas, much better than most of Eastern Europe and Africa, and at similar levels as "rich" countries such as Italy. So try to put a little perspective into things instead of spouting the same blabla to non-Brazilians.