1) If they actually made it two weapons, they would have to adjust drop rates (likely removing a ranged weapon drop off a boss) for it and I, and many other hunters, don't want to have to try and get two weapons when sometimes just getting one is hard enough.
2) If it was actually two different weapons, they would have to redo all the hunter attacks to balance them around 2H ranged and dual 1H ranged weapons. This would lead to balancing issues and theorycrafters would find out which is best and everyone interested in raiding progression would go with that.
3) Whether it was actually two separate weapons or a single weapon that had a dual wield animation, they would have to redo all the attack animations for every race and for every possible transformation (potion, buff, silly toy, etc....) out there. That is far more work than most people think.
I think the vast majority of hunters are not interested in seeing Blizzard pour dev time into making a purely cosmetic change that only a small amount of people would really like to see happen.