Why don't more players skip the MLB draft?

With all of these guys coming out of college and demanding big money, why don't they just not enter the draft? If they have a lot of talent, the big teams can sign them and they won't have to worry about being drafted by a team that "can't afford" them. If the top players from places like the Dominican Republic can enter the league as free agents why don't the top college and high school guys? From a top prospects standpoint it seems like the better decison so you won't get stuck on a team like the Nationals and you can make your money.