He's not lowering tax to make himself richer, he is very very rich, so rich he turned down the presidential wage and gave that money back into the budget, he's primarily lowering corporate tax in order to bring American companies back into the US in order to make all those jobs being given to foreign employees back to the american people. I'm not happy about it as IBM and Apple and many US companies give people in ireland thousands of jobs over here. But when you look at the big picture he wants American corporations in america giving jobs to Americans. Is that really a bad thing?.
As it stands US corporations make more profit from the Irish tax offers. Trump just wants to get them back in the US, it's the primary reason for lowering corporate tax not his own profits.