Marketing. It is stupid easy to sell rockered boards to beginners or people who don't exactly know what they want.
"Rocker makes it float easier in powder, you'll catch less edges, and you'll be able to press easier than a cambered board, blah blah blah." A simple sales pitch like that will make 80-90% of the people walking in your door stoked on reverse camber.
However, it's a trend. Preferences are already shifting back towards camber, for the past few years. Capita's most proformed (read shop employees, mountain employees, generally people who ride much better than the average person) board from 2-3 years ago was the cambered Indoor and you can see it in companies' line-ups. For example, Lib Tech, for all their blustery points about only making rockered decks, have essentially make a cambered board (albeit through a different name).
FWIW, I'm a camber kid.