How many of the ones who got a chance to move up, asked to stay down with their team mates? Nobody pulls a Matt Leinart once they go professional. It doesn't happen too often in college baseball but there are players who will turn down good money and risk their dream of playing pro ball to stay with their team one more year.
Loyalty to the school is a big deal in college and it doesn't end. It isn't perfect and players do switch teams. In pro ball there should be loyalty to the team you are on but let's face it pro ball is a business for both the organization and the players and loyalty to the team is limited. There are players out there playing with the goal of getting a look from another organization because they know there's no room in front of them in their own organization.