Level rewards.

[Gothika]

Originally Posted by Draenin

I almost got to level 30 magic before getting sick of doing my immenses, and I could wipe the floor with Brigid. It was mainly because, at level 110, I could fully enchant her relics.

You see, people don't go past level 30 because its not worth it.
At level 30 you have enough mana and your spells are good enough to kill.
If there was some greater reward at the end people might level magic more.