ExPo has an article on it:
http://expeditionportal.com/trail-tested-jeep-grand-cherokee-ecodiesel/
I'm going to go out on a limb and say it's because they don't look like an off road vehicle, more like a soccer mom crossover you shuttle shopping sacks to and from market with.
Overlanders dig their kit. Not many places to bolt junk onto an aerodynamic body. Like you mentioned, not much aftermarket support for bolting junk onto an aerodynamic body. Therefore no enthusiasm. People might be overlanding in them, they are taking photos of the landscape, not of their ho hum nothing special here vehicle that gets about as much media attention as a household appliance.
While it might be capable, it's not going to be the stand out and look the part rig, thus you won't see much enthusiasm here over them. Does not mean you couldn't do a lot of traveling in one.
That said, Jeep's poor reliability past, (and even Doge, Chrysler, whoever owns it all overall's past reputation matter of fact) has detoured me from ever considering buying anything made by Jeep seriously. Same actually holds for Ford and GM as well. If I'm looking for a reliable vehicle I immediately start searching for an import (Toyota or Nissan specifically....) That is kinda how reputation works, and it will take a while to recover that even if these newer Jeeps turn out to be the most reliable vehicles ever made, sad, very sad, but true.