I recently did my taxes. I did marvel at the questions, "are you a minister? Do you own timber land? Are you a retired firefighter? Did you set up a fund for sustainable research activities? etc etc". 

As Robert points out, the tax code has power to punish and reward. Everyone has skin in the game, so hate to lose the bonuses they get, even if they would pay less with simplification. But it remains a prime area for lobbying, exploration by the rich and simplification would be one of the better ways to remove the "bought" advantages of the wealthy.