Hey GoodisBeer,
There are several reasons that I can think of. 1) To increase the hop utilization, a lower gravity wort means better hop utilization. 2) Lighter beer color. With a high gravity wort, the sugars are more likely to caramelize or scorch producing a darker beer. 3) Less caramelized flavor allowing the yeast, grains... to come through better.
I have switched over to DME for the reasons noted above and my beer quality went through the roof. Even with DME, I still do a late addition.
There are some that will disagree with me that DME produces light color and lighter flavor beer, however my side by side comparison shows me otherwise.
See for your self
Toy4Rick
