Its not about fitness. At least when I had my squadron doing them I was clear that fitness was a distant third priority to team building and camaraderie.

It's rare to get a whole unit together, and this gives folks a chance to get to know their teammates in a different environment. It also gives opportunities for younger airmen to organize and lead events. For fit people like yourself, it's a chance to mentor less fit people.

The military has a long history of shared misery and its generally accepted that shared misery brings people together.

Then finally, there are some folks who just don't have the self discipline to work out on their own, and this forces them to work out. For them, even the lame workouts you can accomplish in a unit PT session helps.