The maps were outdated, ugly, and complicated the code (from what I've heard). The new lighting system was implemented when maps were removed. Sadly enough, you now need to build a map for servers in the building game. If you really want to have maps, you could migrate to the v20 server that was rigged up, if it's still active.
Coming from BL_ID 7307, who is ok with maps being gone.
this doesn't meen I don't miss the old maps :(