Tight budgets simply won't allow for it right now:
Nation building in Iraq and Afghanistan was very expensive, and many of the funds were lost due to corruption and waste. The governments of both nations are a very long way from being stable or democratic—and their alliance with the West remains untested. The Obama strategy calls for any future nation building to draw on large conventional forces; in effect, it seeks to rely on offshore balancing of the kind that worked well in Kosovo and Libya and is now attempted in Yemen. Some in the Pentagon will keep fighting for a counterinsurgency approach, which includes a strong element of nation building rather than counterterrorism, but given the budgetary pressures this plank is most likely to survive—and for good reasons.