Supply and demand as well as the logistics and overhead required to sell and support a boutique market product (that happens to be quite bulky).
I am in the market for a RTT and am pretty sticker shocked by them but as a business owner that sells boutique products myself, I get it.
That said, as the popularity of these things continues to grow, prices will continue to drop, eventually to the point where a few big companies move in and undercut the little guys, replacing margin with volume. I have seen it time and time again in my field.