Tell me, why exactly does my fire mage have 60k less hp than my frost mage

I noticed that when I took a deeper look how much hp the average lvl 90 player has. 200-230k. I saw my fire mage has just frickin 150k hp, so I swapped to my frost mage specc and it went up to 210k. Like, why is that? Is it to balance out the "brokeness" on fire mage in pvp or what am I missing here?