My views on the D&RGW's popularity are basically stated in the "love" thread...
First and foremost, a single NG Tweetsie locomotive survives. It doesn't run on the original roadbed. It does not have any of the MoW equipment that rail fans gush over. It doesn't have a 40-50 mile long railroad to pull excursionists over. It doesn't have the majestic, modern Stemwinder passenger train of the 1920s-30s.
For around 60 years, the Silverton has been creating converts to the NG orthodoxy. It has introduced millions to 36" gauge trains. To a rail fan, it is all the more overwhelming because there are so many locomotives, cars, miles of track, and railroad structures...even if there isn't much variety. In short, it is very easy to learn about the D&RGW...it requires ZERO effort.
I offer a slight variation on the question: why do 90% of D&RGW fans seem to exhibit no interest in the D&RG? I presume to answer this as follows: they have experienced the D&RGW, while the D&RG is in the distant past.
Michael