Because you will not have a life if you are a neurosurgeon. You won't make "huge money" if you work your ass off. A "relaxed" pace for a neurosurgeon would cripple a lesser man.
That being said, I personally have a lot of fun doing neurosurgery. Not fun with the money I make, not fun telling people I'm a neurosurgeon, I enjoy the art and science of neurosurgery. It's like being in the Night's Watch ("I will take no wife, hold no lands, father no children"), your life is your work so you better love your work.