A very small percentage of people can do what professional athletes can do. Baseball is the only sport that a player has to be able to hit, catch and throw a ball. Its kind of like supply and demand. If many could do it, the many wouldn't be making anywhere near 16 mil per year. Baseball and other sports are entertainment, and people love to pay for entertainment. If they didn't there would not be any professional sports.
The nice part about it is, if anyone thinks they are good enough to play professional baseball or any professional sport. they can go try out, and if they think you are good, you will make the team and they will pay you big money depending on how good you really are. Just think, if you are really good you could make 16 or more million a year.