A couple of reasons. One, I'm pretty lazy and don't want to convert clothes to new figures, or mess around with DSON. Two, about 75% of my renders involve characters I've played in table-top RPGs, and making a picture with one of them is a little like getting to play them again in a game. Most of these figures I've developed V3 and/or V4, M3 and/or M4 versions of. I'd much rather spend my time building a picture rather than rejiggering a figure.

 Also, particularly with some of the fix morphs (and the couple of times I've tried weight-maps) they bend well-enough for me, since I tend to use portraits of clothed figures. I've also avoided DAZ Studio (although I am tempted now, with the integration of IRAY, and the improvements to G3) because I understand Poser, and I don't want to have to go back and download all the DAZ Studio versions of my content.

I also find that I'm not nearly as much into photo-realism as I was.