I haven't skied there in a long time, since I lived nearby, but I will take a crack at answering.
Mad River has with good humor played along forever with the whole "Ski It If You Can" schtick. It aligns well with the reality that a majority of their terrain and snow conditions are too much for the casual skier of modest talent and ambition. Not to mention the low throughput of the single chair. Yes, they have a pod where the grooming and terrain are great for beginners, but its capacity and snow reliability are limited, and it's already well populated by local devotees. Basically the skier population is highly filtered. Joe Skier goes somewhere else.
Castlerock is its own little version of MRG embedded within Sugarbush, with skier population filtered by some of the same factors such as lift capacity and terrain difficulty. Joe Skier goes elsewhere on the mountain.
Smuggler's is not really all that different from Mad River in terms of its lift capacity and terrain. Meanwhile it makes a point of trying to attract vacationing families and the local general skiing populace. Unlike Sugarbush, it doesn't really have anywhere for that crowd to go, with the exception of Morse Mountain, which gets old pretty fast if you're there for a week. So they do the best they can to groom the whole mountain in a way that makes the terrain as accessible as possible, with only modest concessions to the hard core. They need to do that to spread the crowds over what limited lift capacity they have. The result is that there really isn't all that much terrain that has the natural and secluded feel you get at MRG or Castlerock.
