For the same reason it would be inappropriate for you to show up at your husband's work place, come up to his desk, and start hanging all over him and kissing him in front of everybody.
As long as you are uniform, the assumption is you are on duty. Which is the same thing as sitting behind your desk at work in an office situation.
First of all, in no way does showing affection for a loved one show weakness on the service member's behalf. It is simply because military members must be professional at all times, in or out of uniform. If you are engaging in PDA, people see that, and it is especially visible when they are in uniform. If they have their lips all over you or stuff of that nature, that will bring discredit the organization that helped make them a soldier because they are expected to uphold themselves in a manner that befits civil society. Civilians may not know this, so this will be a reflection of what every Marine does.
to see a dude making out with a chick would not make him look very professional now would it? A peck and hug is fine, but grabbing boobs and stuff and having tongues going crazy is a bit too much.
First of all, anyone in uniform must be professional at all times. You represent the military. It is considered displaying unprofessionalism when showing PDA. Oh, don't get me wrong we love the PDA and want it but when in uniform you just keep it under wraps and wait until you are alone or away from the unit, or even wait until you get home. Sorry, just being honest. I am prior military myself, so I know how hard it is to not show PDA to your boyfriend or husband and I am a female. It is much harder for us women because we are so use to showing our affection and love, especially when we are proud of them. But then again it is truly tough on the men also, because they really want to be able to embrace their girlfriend or wife when they have accomplished something such as an award or something. Anyway, just take a deep breathe and save all your hugs and kisses for later. He will definitely be awaiting them I'm sure. Best wishes and hang in there you can do it.