This question is in the same universe as my last one, How to raise an army against the dark lord when everyone thinks he was already defeated? In this universe, magic is powered by the energy of thought, and if you don't have enough thought energy stored somewhere on you, spells will drain your energy, killing you in the process. After the Dark Lord from the previous question was defeated for the first time, remember the story takes place after the second time, he left the world in a post-apocalyptic state.
Why would anybody risk using and learning magic, if life is just a constant struggle to survive, and learning magic just adds another way for you to die?