Very good question. I was about to post the same.
AFAIK, the gate guards do have ammo for their weapons, so when a vehicle blows through the gate stop they should have perforated that vehicle.
In my experience, it could have just as easily been a seriously inebriated soldier coming in., a mom in labor... . For the shoot first, ask later crowds.. that is irresponsible, please tell me you don’t carry. Police officers and any responsible human should do a threat assessment prior to pulling the trigger that ends a life. Military bases have various levels of conditions and I doubt we would want them to stay in shoot on site security.
They probably aren’t that good with their weapon anyway. And I doubt they carry one that can disable a vehicle, regardless of what Hollywood tells you.
Army bases vary in openness. When I drove to Bragg I didn’t realize I was halfway through the base, as there was no restricted gate on the road I was in.