Why lock the doors when boss is pulled?

Purely out of curiosity, does anyone know the gameplay reason for locking the doors to a boss fight in a dungeon once the boss is pulled? It's not just to prevent people from running back after dying, since the "release" button is already disabled during the fight.

I ask because this mechanic can be (IMO) abused in some cases. Last night I was doing a PUG ToP (normal or heroic) for the weekly dungeon quest, and the tank clearly wanted to finish the dungeon as fast as possible with absolutely no concern for anyone else in the party. One of the other DPS players got knocked off That Platform, released, and ran back -- but the tank pulled Kul'tharok before that DPS could catch up, and that disables all of those portals for the duration of the fight, so he was locked out. Now, there's not a change to the game that can fix the fact that the tank was a grade-A jerk, but I am sorta curious about the potential consequences of removing this lockout.