Well, yoyorast's purpose of the contest is to promote the map.
Let's say you never even heard of Halo CE. And let's say you never played custom maps (like console users).
If you see a video that is very short about it, wouldn't you want to know more about this map? Usually the longer the video is, the more places you know about.
t3h m00kz shows many places in the map, and it is long (which makes it a great video).

Also, yoyorast 2 is a huge map... If it's a short video, i don't think it shows enough features of the map.

I say that the voters still choose, however, a longer video is probably given a lot more effort and time.