This idea has already been visited on, and it failed. Too costly, etc, etc. But I will throw in this.

While it is true that the majority chooses escape maps, a minority of these voters know what they want and truly want to go to these maps. Some facts about the zombie mod server....
-The server has 30+ players usually from 10am-10pm. Exclude special occasions
-Any other time, the only people that bother coming to the server are mostly regulars or foreign people
-Whenever the server has over 30 players, the majority of them are (ignorant) non-regulars

That being said, they're just clueless ballot-stuffers.

For those who don't play zm, you might ask why these ballot stuffers choose ze over zm. Lots of ze maps share two distinct characteristics. One, the gameplay is awful (either because of lack of teamwork, exploitable, glitchy/poorly made maps, or awful ideas overall). Two, they have names that appeal to the eye of those who don't know the horrors of playing it. For example: ze_hellescape, ze_titanicescape, ze_canalescape, ze_aperturescience, ze_lostworldredux, ze_paradise, ze_indianajonesescape, ze_grandboatescape, ze_jurassicparkstory. Appealing names coupled with failing gameplay.

Furthermore, lots of these non-regulars are incapable of building themselves an effective barricade. Thus, these non-regulars will mercilessly use their !maprate vote on decent zm maps that lots of us regulars like, and bring its rating down. Consequently, these maps will appear less and less and further down the voting options. Therefore, escape maps will fill the voting board more often. The best friend of the clueless ballot stuffer is "spam first option as much as i can."

Clearly, it's no wonder that these ze maps APPEAR to be more popular with the voters