They wanted to experiment with it. JD is a DJ (see what i did there), too, so he thought it might be an interesting idea for a musician. I don't dig it, I can't really get into the whole dubstep thing, but I still respect it for what it is, an experiment.
Korn is actually trying to get away from this particular template. Bunch of bands tried to be like them, almost copied their style. They experimented a lot just to stay unique, what they will always be in my opinion.
But anyway, I'm an oldschool fan, with a little bit of hope that they get back what they do best, doing freaky nu metal.
Edit: @ jack: Dunno', Ray isn't a valuable member in my opinion. His style doesn't fit Korns music, he can't write for crap.