I believe it is our reward system. Sure, people will chose enjoyable activities over what they perceive as work. However, if the reward system were changed so that people either worked or starved, they would probably chose work over starvation. Fear is a great motivator. Of course, I have over stated the "solution" to make a point.
My mother was my greatest motivator. She was barely 14 when the Great Depression hit and from a large immigrant family to boot. Her rationale for working hard was, if you don't work hard, you won't make money, and if you don't make money, you will starve to death. That was usually in the context of losing a job, but the message was clear. She never raised her voice, complained about my grades, or anything like that. She simply instilled the fear that I would stave to death, if I didn't work hard. I probably heard it every day. Not much more was needed. Today, starvation is far less real than it was in 1929, and there are things I enjoy doing, but work has always come first, even now that I am retired.
So, I don't think it is a question of what a child will enjoy doing. The answer to that is obvious. It is a question of what the child feels he needs to do. Do we give our children too much hollow praise for just getting by, thus diminishing the fear of failure? Perhaps. A good and very successful friend was once asked why he didn't praise his employees as much as others did. His response, "the absence of criticism is praise enough."
John