I am not a wildlife biologist, but from what I have learned, survival of adult female ungulates is the most important factor in ungulate population increase vs. decrease. It is also much more difficult to determine sex of mountain goats based on horns or antlers than most other ungulate species (exceptions include bison, caribou, bighorn sheep, and sometimes pronghorn). I think the reason for many goat tags being either-sex vs billy only is that most people don't get a lot of goat tags in there lifetime or even see many goats, so they are not good at determining sex based on physical characteristics. Game agencies also do not want to create a lot of well-meaning criminals so they give out either-sex tags. Just my opinion based on a lot of research from someone who does not get paid to do it.