U.S. tax law structurally incentivizes contractors to favor overseas bases.

Evidence

Because U.S. corporations are taxed only when they repatriate such foreign earnings, the current tax system encourages companies to earn and then keep their income overseas. This congressionally enacted structural incentive applies to all industries, not just military contractors. However, in the case of contractors doing work on U.S. bases overseas, its significance extends far beyond lost tax revenues. Given equivalent contracts to provide services on a base in Texas and a base in the United Arab Emirates, for example, the base in the UAE offers significantly more options for indefinitely reducing U.S. taxes. In short, the U.S. tax code actually encourages contractors to support the stationing of bases and troops abroad rather than at home. — David Vine, Base Nation_ How U.S. Military Bases…, 731