Yeah, Marian body armour looks pretty good, doesn’t it? Stormtrooper armour looked good too. But instead of something to deflect laser fire, protect against physical attacks, it’s just plastic. But the Stormtroopers, and the Marian soldiers for that matter, aren’t meant to know that. Otherwise, they might not be so quick to volunteer. Besides, seeing troops walking down the streets of Nova Roma makes it look like the Hegemony is spending their tax money wisely, rather than wasting it on road trips to Canopus.