Somehow I gotta believe that who ever set up this forum did so based somewhat loosely on the laws of supply and demand.
Take the bowhunting forum. It is largely an offshoot of the deerhunting forum as deer hunting dominates that forum to (but they do bring in other species to discuss). It could have just as easily stayed in the deerhunting forum. However, the demand from the bowhunters was high enough for the forum mods to create another forum where bowhunters could have discussions that were not pertinenet to gun hunters.
Now I am sure that if there was enough demand for a muley forum the mods would likely do so. Problem is that as much as you like/love muley hunting it obviously ain't so popular on this messaage board as you would like. Having a muley only forum that get a two or three posts a day is hardly the demand the mods will waste their time on. In short the mods seem to do a decent job creating avenues for us to discuss things if the demand is there. Obviously muley discussion are low on the demand side so there is no supply.