These guys aren't in some kind of parade or ceremonial display, nor do they appear to be at a guard post.

They're just soldiers standing by. In that situation there's no need for a uniform display to impress anyone. Keeping soldiers at drill precision 100% all thetime is a good way to fatigue soldiers who don't need to be perfect quickly.

Besides which, all of them have a hand near their trigger guards and most have hands resting on the barrel of their weapons so are reasonably prepared if someone does try something.