Because people come up to them and thank them for their service (and buy them drinks).
This is a military town, so sadly, no one really looks twice at the uniforms. We have Yuma Proving Grounds and MCAS Yuma here and there is some kind of Naval Station in El Centro.
And people always know my dh is a Marine, even if he isn't in uniform because of the haircut, so he wouldn't need to wander around in his cammies LOL.