Maybe the sportsman or the piano player ends up earning a lot of money, but I assume, only very few start doing a sport or playing the piano with the intention to become famous and earn a lot of cash. Everybody tries to improve themselves in the things he does - some take it a step further and try to become the best. This is absolutely not limited to musical instruments or sports, you can see this in nearly every aspect of live. Have you ever read a little in the guinnes book of records? There is a whole bunch of records, noone would ever pay them money for. Those people only did it for the fun and to become the best in their respective area.
Whenever there is a possibility of competition coming along with a broad base of people to compete, there will be people who try to maximize their success and become the best, no matter if there is any prize to win.