Answers:
Because it requires us to work hard for what we want. Humans like most members of the animal kingdom, naturally would rather have something nothing or take the easy way out. For example a dog would rather have someone feed him than have to hunt for food. This is why you see stray dogs destroying people's trash instead of hunting down squirrels. Secondly, for many of us, in school we seem to be required to learn what we don't feel we need to or want to learn. For example, I am a pre-law, and my degree plan required me to take a visual or performing arts class. Why do I need to learn about the history or dance or sculpture to become a lawyer? But nevertheless our drive for success surpasses the boredom of doing busywork and the frustration of dragging ourselves out of bed at 6 am to listen to a dull instructor, when we would naturally rather lay on the couch watching soaps while our parents take care of us forever.
Anything worth having is worth working hard for.