They fetch high prices because a lot of people want them.
Well, a lot of people may want them, but there's not a lot of people bidding on them at these prices. From the bids that I've looked at, there's only a few of the same bidders, and most, if not all of them are members here. And those who are bidding them up already have a stash of them, so it's not like they need one to use. Don't take this the wrong way, I'm not complaining at all, in fact I'd do the same thing myself if they were selling in a range I thought was reasonable.
I do think it's important to differentiate between sales on eBay and sales on Geekhack. I've purchased four regular SSKs in the past month. Three of those from Geehack members. The average price I paid was $110, not including shipping. In March, jpc sold his pristine condition bolt modded SSK via Geekhack. He didn't say what he sold it for and I wasn't the buyer, but based on his post, I'm guessing $175ish. Had it been in just average condition, I would assume it would have gone for much less. So I would say that based on the most recent data, average condition used SSKs selling on Geekhack are way below the $200 point. Ebay sales are high profile sales reaching a much larger group of potential buyers, so naturally you'd expect those prices to be higher. However, being most if not all the bidders are members here, it's a bit strange as well.
The way I see it, businesses, such as Clickykeyboards, that are in the business of selling keyboards are charging full retail prices. Keyboards selling on eBay are on average selling for the market price. Keyboards selling on Geekhack are selling on average for a wholesale price. Lots of reasons for this, not the least of which is that some people feel a sense of community here and aren't out to make the maximum profit. I know I've bought a lot of stuff for much less than I would have paid on eBay, and when it comes time to sell, I doubt then I'll try to get eBay prices. We all give and take via the Geekhack community by offering our advice, experience, etc. via posts. So it's only natural that we do likewise when offering items in the Geekhack Marketplace. When I buy something off of eBay, I view it as strictly a transaction. Once the deal is done and the keyboard is in my hands and as described, the deal is finished and I pretty much forget about the seller. When I buy something from a fellow Geekhacker, I feel like it's much more than just a transaction. It's like there's a connection made at the same time. From that point on, whenever I see them make a post, I always think back to the keyboard(s) they sold me. Perhaps I'm just weird, but that's how I view it.