I stopped by Black Widow just last week and was talking to them about this very subject.
They told me the reason they went to that style was for the bow to be more stable.
They had me draw a bow, then try to use my bow hand to twist the bow.
The limbs on the belly side makes it harder to torque the bow, than having the limbs on the back side. I tried it with their SAG, compared to one of the belly mount bows. There is a big difference.
It is more stable, but I sure don't care for the looks very much.