If people nominate maps and then leave, the map gets un nominated. It's really not that hard of a system to figure out. If you nominate a map, and stay to play, it will appear on the list, along with 5 or so randomly generated maps (unless you have that many people nominating different maps, then it's just first come first serve). Having a bigger list won't do much as Phil has pointed out, people get the first comfortable map they see and spam it. That way they can have it off their screen, and back to staying alive/killing.