The problem with that is that closing or freezing an island will lose players from the game. Some players only choose to play on one island and don't use their full playable character quota. Furthermore, some other players have such an attachment to certain islands that losing the ability to play on that island with see their interest in the game diminish (several players have said that on the forum - and that's not even taking into account the bulk of players who never post on the forum).
There's absolutely no guarantee that closing/freezing an island will increase player density elsewhere. Basically, it comes down to either finding a better idea or rolling the dice on the closure/freeze and hoping it has more of a positive impact than a negative one.
