Clad in corroding armor plates, some Champions contain their bodies to prevent guts and rot from spilling all around. They carry armor not just for the sake of protection – layers of rotten flesh and nurgles gift are providing resilience far beyond any conventional armor – but for mobility.  At a certain level of decay, armor becomes less encumbering than carrying none. 

Especially if demonic strength provides power and endurance of unimaginable plenty.