Military bases are surprisingly big. They usually have many civilian contractors, traffic, and many uniformed people who are not really intended to fight. Cooks, mechanics, and barbers are some examples. Additionally families are frequently mixed in. As are stores and facilities to accommodate them. Sadly, unless a base (not all bases) is on alert, in many cases even military police at gates are armed but not issued ammo. There's a general policy in the military to keep as many people disarmed as possible. So as strange as it sounds (I agree with you), most military bases make for good targets of opportunity. Which is why large shootings have taken place at military bases. Including a Muslim terrorist attack under Obama.