It gives them a chance to play a kids game a make a lot of money. Otherwise they'd be mechanics, lawyers, doctors, etc, etc..
What they give is money hungry power trip idiots millions of dollars. Who gets the better end of the deal? MLB and the owners make a LOT more then the players. And the players that do make millions are OFFERED that money. No one forces owners to pay it. But the fact is that without the players, there would be NO MLB.