Well you see this in pretty much all apps/styles of CG, nude and semi nude females are the number one choice of subject for the largely male userbase. Forgive us, we cant help loving renders of nekkid women in seductive poses... ;)

Also i feel its not imagination thats lacking but time and resources. Mastering even one area of 3D takes a huge amount of effort, and for a decent looking scene you have to master multiple areas as well as art theory. ie for the average person who just wants to use poser for fun, it becomes quite a long and hard journey to get to that kind of level. So what are they supposed to do in the meantime ? I suppose they could wait till they get good enough and then start posting work, but IMO its much more interesting to see the progress of an artist as they improve and change. Sure along the way there will be plenty of boob infested pics, but that's all part of the fun no ?