Defense benefits bears less than other tanking classes. By contrast, agility benefits us much more. So unlike warriors or paladins, we often want to stack agility instead of defense. And we can afford to use resilience instead of defense for crit immunity more than our plate-wearing friends.
The math isn't too complicated. Let's compare the new Steelweave cloak enchant (+12 defense rating) to the old Agility cloak enchant (+12 agility)
Bears
+12 agility = +0.82% dodge = +0.82% avoidance
+12 defense rating = +0.20% dodge, +0.20% miss = +0.40% avoidance
Warriors and Paladins
+12 agility = +0.48% dodge = +0.48% avoidance
+12 defense rating = +0.20% dodge, +0.20% miss, +0.20% parry, +0.20% block = %26gt; +0.60% avoidance
The result is pretty clear; from an avoidance perspective, Agility is better for bears and Steelweave is better for warriors and paladins. Of course a bear might still choose to take Steelweave over Agility if they need the defense to become crit immune. But consider the wrist and chest enchants first; that +12 agility is really good.