Clearly it's because he is offering to bankroll a supra-national group of elite soldiers to fight the alien menace that threatens our species and way of life, a

Clearly it's because he is offering to bankroll a supra-national group of elite soldiers to fight the alien menace that threatens our species and way of life, and he is hoping that "[Musk] has been chosen to lead this initiative. To oversee our first—and last—line of defense. His efforts will have considerable influence on this planet's future. We urge you to keep that in mind as he proceed. Good luck, Musk" - X-COM:Enemy Of Tesla