wow kinda reminds me of the same thread i posted awhile ago. You should try the search bars and see what they said.
This thread was started in 2009
And bagrat read on how our solution came to, a map that was voted upon would be placed in a black list. That black list is a list of recently played maps that will be uneligable to be voted upon in the next 3-5 map rotations. After a cycle that map will be placed in a green list, in which 3 maps at random will be selected to be voted upon.