What does FPS games have to do with anything?
I can think of plenty FPS games that dont even use ammo, guns are just infinite.
They dont do it this way because there is no way an unlimited shock staff would be a balanced mechanic.
Swords break down, mana runs out and so do potions, spell scrolls and enchantment charges.
This is the way the game works and its a good thing, it adds an element of strategy.
The very last thing we need is even more simplification.