Same reason.

At rendo, there are a lot more poser users so they are using V4, but there are some pose and prop sets that have support for V4/V6 as well. There is also more outfits that fit Genesis 2 female here. Genesis 1 didn't catch on as well here. At DAZ, customer demand for Genesis 2 basically pushed V4 and Genesis 1 out of the store for the same reason, where the releases of Gen 4 stuff is few and far in-between. More prop sets and environments are DS native (.duf format rather than pp2) at DAZ as well.