Earlier quoted context omitted.
Locks are often intentionally omitted from equipment in environments where high availability is prioritized. They are also often omitted in locations where physical security is provided at a broader level.
Sure, let's intentionally omit locks from equipment that is designed not to fall into enemy hands. Let's not have a kill switch, either. Sure, makes sense for an agency with more money to spend than every corporation in America!
Slow down there with the sarcasm and think about the actual requirements or use-cases first. Your average operable military vehicle is in one of three situations:
1. Actively occupied or guarded from theft by current owners/operators with guns who will not tolerate strangers getting close.
2. Parked somewhere in the middle of a whole bunch of people who are generally guarding the whole area, and those people may need to be able to operate it very quickly.
3. In some long-term storage which is well-fenced, under surveillance, guarded by people with guns, and typically very far from both overt enemies and opportunistic thieves.
So there's already an access control system tuned to a particular set of needs... and one of those needs includes "using it to escape from something dangerous even if the prior-driver and everything in their pockets got vaporized."