His spells cost 0, why would he need magicka?
You can easily get magic damage resistance up to 97%, you have illusion and conjuration so you never get aggro, why do you need health? Theoretically you never need to even level up, if you power game it.
Like I said, if you think grinding enchanting up fast and putting on a full set of gear that you make is a good idea, you don't need magicka. However, then you are stuck with that gear or you are useless. But not everyone wants to put full perks into enchanting and go around hunting mudcrabs to fill soul gems. If you are playing in a more "normal" way, magicka is more valuable than health because it gives you more options in a fight, and so long as you have some magicka left you can usually avoid taking damage.