The US IT sector is heavily subsidized. Giving Apple, Google, Facebook etc. billion dollar subsidies at home would spur trade wars. So instead the US uses its never failing ability to play European countries against eachother and its influence over smaller jurisdictions like Ireland, Netherlands, Switzerland, Guernsey, Jersey, Bahamas, Isle of Man, British Virgin Islands etc to make sure that large US corporations' foreign income - which wouldn't be taxed in the US anyways - can be kept untaxed.