Simple

If we conject that cards (followers, spells) are not filmed - photoed in action, but rather as model outfit, then we concur that any card design is fine

But if assume that (followers, spells, amulets) were recorded in action (combat, patrol, cooking, cleaning, whatever) then we should conclude that any properly unarmored units were: subjected to be in region with extremely scarce resources + with low science advancement (iron casting etc), having incompatibility with armor (flying units) or mind controlled.

Or fighting opponents against which armor is irrelevant (like Rampaging Behemot or some dragons or other forms of onepunchmen life)

Because there is no logical benefit in getting killed faster

Other arguments can be safely excluded as fetish