Because The Guardians of the Tomb of the Unknown don’t need bullets to annihilate evil. One glance - a break from their perfect drill - is enough to fry the mind and soul of a Jihadist and send him to Hell forever.
Only gay members of the armed forces are issued live ammunition. That is done to prevent attacks from gender normative evangelical Tea Partiers.
This works because our POTUS, a gay fellow from Kenya, has made it clear to potential foreign enemies that he will personally drive them mad with equivocal non-stop nonsensical statements if they try any funny business. He has also said that "he will stand with the Muslims," if push comes to shove. So, we will have no need to take pot shots at his Muslim pals. Indeed, they may well join gay members of the armed services to protect our nation against Tea Partiers, racist militias, and white lynch mobs.
Also, Pentagon researchers have found that traditional infantry weapons are largely ineffective when battling viruses like Ebola, not to mention being hard to operate when wearing a hazmat suit in 130-degree temperatures in the African bush while building hospitals and clinics, and taking care of infected patients. This use of the military is being carefully planned by Team Obama. Each service man or woman being sent in harm's way is to receive 4 hours of intensive medical training, a bottle of hand sanitizer, and will be billeted for two nights in a Holiday Inn Express near the departure airport.
This careful planning is why they pay the Soetoro Boy the big bucks.