It's probably outside the limits of what can be done on the server side, but is it possible to disable the ability to click on a map that has already been voted for. Make em use the gawd damn list to vote.
Not without rewriting the vote handler...its probably not worth the time.
Besides, like last night when there was a spirited political discussion (it stayed civil mostly), and no one voted and we had to play All-Fall-Down which most complained about -- but they didn't vote lol. Some complained they wanted it removed because it sucks.
We did a get a mid game vote initiated though (if half the players vote it will change the map to the highest voted)....
Mostly though, I am of the opinion its just laziness. Lazy to scroll (and you can sort the map by name, sequence, times played) and vote. And worse yet lazy to learn newer/other maps.