Some people are leaving partly to pay more tax. Sometimes the spiral downwards of paying less tax can be bad for society. eg raises poverty line.

But you don't pay double tax on overseas earnings unless the overseas country requires you to pay less tax than in the US as long as you file the tax return, or at least that was what was written in the article as far as I could tell, so the only people paying more are doing so by not filing and being fined.