2x123 used to be the bottom level of flashaholicism, thus the larger EDC size. My first EDC lights were huge by the standards of this board. I used to carry these lights in my right front pocket (not at the same time):
-Inova T3
-Streamlight TL-3/TL-2
-Pentagonlight X2/X3
I never had a problem with it, I really guess it depends on what you wear.
Nowadays I EDC a D-Mini but am not adverse to larger lights. 3x123 is pretty much the limit for me. I've noticed the trend too and just chalk it up to the greater availability of well-made, bright AA, AAA and 1x123 lights.
Remember, it wasn't too long ago that there really weren't any good 1xAA or 2xAA lights since LED was still young and incan shuns alkaline. There used to be dozens of newbie G2 threads every week since it was the entry light. 65 lumens used to be the sun for new members. Then Fenix came along and LEDs grew up and everything changed.
I'm betting the new user now goes with some sort of 1x123 or 1xAA light as opposed to the entry level 2x123 light of yesteryear..