For all *wizard* builds. Because Wizards have pathetically bad *other* defenses. Best slow is 60%, worse than 80% that both DH and WD have, and costs a big chunk of damage dealing resource. Frost Nova lasts very short time on inferno elites with long cooldown. Wave of Force same deal. Diamond Skin not scaling, so 1 hit removed. Teleport long cooldown. Stacking res/armor/vit is not an option for Wizards.
A well geared Barb or Monk can survive, somewhat. It isn't a straight up facetank, but with gear it is possible to live. A well geared Wizard without Force Armor cannot survive, at all. No amount of vit/res/armor will change that.
They can? Show me the Barb or Monks that can take 3 hits and live on Inferno Act 2 or later.
The fact that you even mention snares on Inferno shows you don't have much experience in this area.