Metalopolis has been around for quite a long time, over a year including beta. We felt that taking it out of the rotation would make some room for variety in the map pool.
Metalopolis suffers balance issues when close spawn positions occur, but becomes too predictable when they are simply disabled. Close positions have been under a lot of discussion lately, and were definitely examining better options to allow for random spawn positions across the map pool without also creating too much predictability and vulnerability to proxy rushes.
Overall balance has also proven to be an issue on Metalopolis -- even factoring in close position spawn issues. Its among the least balanced maps currently in the ladder pool, and along with Scrap Station (also being removed) and Taldarim Altar, has a heavy (60%+) bias toward zerg at the highest levels of play.
If Metalopolis makes a return to the ladder pool in the future, it will likely receive some balance tinkering, much like that administered to Lost Temple which resulted in the creation of Shattered Temple. In the meantime, we hope that you enjoy the fresh maps that have been added to the ladder pool in Season 3.
