It will take a couple iterations of moves to compact people in to the middle. I am noticing a couple mines appear but they will be filled with someone on the outer rim at the next iteration if a person has the boosts to fill the spot. Those near the edge are waiting for spots to be vacated in the middle or new neighbours. If your on the edge now you do get priority to move into the middle.
It takes time for the safe harbour inactive towns to move out which also impacts this.