IF you make every player a free agent after three years then

(1) Noone can really rebuild because by the time they get the players together to take a shot at it they would be free agents

(2) You'll totally take the youth factor out of the equation for teams building. What difference does it make that Lance Berkman is 14 years younger than Barry Bonds (when trading) if I have to give up Berkman in 3 years anyway.

(3) You'll need a free agent draft thats a lot more rounds.

(4) If you have to turn over 90% of your team in 3 years there is no incentive to build and tailor your team the way you like it because you won't be able to keep them.

Effectively you would be taking a lot of the team building strategy out of the game.

If people want to turn over their entire roster that fast they should go play launch leagues.