I get it, people want to use robes on a mage, but this is assuming you guys are never gonna get hit.
"This is assuming" or "YOU are assuming"? I don't see any one "assuming" any such thing. If you have more armor, you'll resist more damage. If you have health instead of magicka, you'll live longer. If you can cast strong armor spells and plentiful healing spells on yourself, or have the perks to use spells from stealth or charm liches, or summon atronachs, then maybe you'll find other ways to avoid damage. The point of having different abilities and armors and weapons and skills is to find different ways to approach the same content. Isn't that half the fun of these games?
What happens when you're in a dungeon or something fighting multiple monsters and you die after 2-3 hits with no armor?
Then you die, and you figure out WHY you died, and you do things differently? And then when you DON'T die you feel like you learned something and got better, and that makes you feel better about yourself, because that's how human brains work.
Or when you armor spell wears off? It only lasts like 60 seconds. What a pain in the ass to have to keep recasting it. The point of my post was that IMO, all things considered it would be better, at least for me, to wear armor and have potions for when I'm low on magicka
So it seems that some people will prefer to wear armor and chug mana pots, and others will prefer to wear robes and recast armor spells. More ways to play the same game? Sounds like good game design to me.