Because it’s so much cooler to be dark-aligned.
This progression almost reminds me of Nanoha StrikerS, where you have so many new characters appear you stop caring for the cast altogether. And for the first time I find myself rooting for the antagonists. One of four gods decide to make his debut. Now if only the other 3 will see the fun of the dark side. 😛
PS. I gave up on remembering the titles of the Flame Hazes and their Guze counterparts. Long, complex and with little meaning. Why can’t everyone be like The Hunter, Friagne.