I agree with CalmB4tehPwn's sentiments. I think it's the case of the price being very high and people being reluctant to spend that much, even if they want the board. The few who do own custom boards either 1. can afford them and already have gotten a few to their exact specifications, or 2. are looking for something specific. Even $200 is too much for the average mechanical keyboard user. So I'm betting there are a number of people eyeing your LZ-GH and either wishing it were cheaper, or wishing it were a different color that they chose, or that it had a different layout, or that it had LEDs because they can't solder themselves, etc., etc. The boards that do get sold successfully through the Classifieds usually stand out in some way, either by reputation (like 456GT or KMAKs, or LZ-SE, or some Hammer cases) or because they stand out in some way in terms of looks (like MistakeMistake's LZ-GH--it would have sold anyway), so those who already own customs feel compelled to add more to their collection.
And on the note of selling--it takes time. You need some good photographs with and without keycaps, good item description, something to explain the price. I've sold a few boards now, and many PMs I get are from new forum members who know nothing about GH's history or what customized keyboards imply, or even that they can open switches without desoldering on some plates. It may take a few weeks, not just a quick auction thread, where it's lumped with other items.
And finally, I'd be in for donating $5-10, as I think it's a worthy cause for a great board. Could have an auction where the price gradually drops as donation comes in, and the person who wants it the most will have to bid sooner rather than later. If they pass, it will go to the next lowest bid, and the first bidder loses their place in line. But I'd limit it to existing GH members with some minimum number of posts. Before you do the auction, you could still try a straight sale, but again, it can take some time and needs some "LZ-GH for dummies" description. Just remember that the market for expensive keyboards is pretty small.