I think it has to do with "generation saturation" (hehe, I coined a term), as well as DCC. (DCC in N and Z scale, that is) As for "Generation Saturation"(C), it's true that a lot of young modellers really have no idea what it took to run a steamer, or the engineering feats accomplished to do so. They grew up around nothing but diesels, and came to accept them as the norm. It takes something special to draw them away. Like for me... it was the Uintah Railway's 2-6-6-2Ts. The uniqueness of the locos caught my attention, and turned me forever. I'm a big steam fan now. DCC in N/Z... It's a size issue. How much room do you have to cram a decoder in that loco? Well, often times, not enough. So... steamers sit on sidings, while decoder-equipped diesels do the dirty work. That's pretty much all there is to it.