It isn't that hard to come up with a decent map design, and the build doesn't have to be necessarily good. It only has to be playable and the design should give players constant action. You don't even have to be a good builder to come up with a decent map, so where did you get that you have to be a good builder to make a good map?
It takes time and effort to make one, but most people don't put forward this effort to make original maps.
The point I was getting at is because people are super-critical of their building skills, they don't want to host what may be a nicely-laid out yet ugly build. Hell, one of my first TDMs was a four-team free for all deathmatch designed for the Ladios Laser pack. Unfortunately, it was ugly as HELL and I got some complaints about it generally because it was easy to fall off, and relatively blandish.
Meanwhile, one build that DID do relatively good around v10-12 was one of those 'castle defense' style maps. It wasn't exactly pretty either, but it was hot during the time (possibly leading back to the 'follow the leader' instance of Knife TDMs during it's time), however I did spend a lot of time of it, and currently I think I got the Version 4 of Zombie Defense Insanity kicking around somewhere in my saves.
As a result, people tend to spurn ugly builds (I got a lot of flack for one of my recent builds, Foundry, and it's relatively empty main foundry floor), even if the gameplay of the DM itself was getting credited. It's a bit of a vicious Catch 22.
We some sort of team death match mod that makes people stick together and cooperate to get an objective complete. Saddly people will rambo no matter what.
Isn't that technically the zombie gamemode(s)? Survive as a team versus a variaty of annoying AIs? Switch players for second team and I can see what you're getting at.
Hrm, an interesting concept though. May have to tweak with that... and try to figure out a way to counter le Rambos creatively.