The guys have pretty much nailed it. Its a niche vehicle. Any time you take something and make it into a trail beater, its market/# of potential buyers gets really narrow.
The more custom/one of a kind stuff you do, to the next buyer, thats more 'what the f*ck is this?' moments. You see how slowly and/or cheaply homebuilt buggies sell for, same thing.
With yours, I think its one step further, that most of the time that people go in that direction with a vehicle, they want something smaller, like a Toyota or S10, or chopped up XJ. Not many people want to trail ride full size Xcabs. Doesn't mean the value isn't correct, just the market is again, small.
I've been trying to sell a decent XJ with some cosmetic damage, can't sell it for nothing. About to switch to parting-out mode.