I think that with such a limited market to draw from, companies and dealers can't afford to build up an inventory and wait for the buyers to show up. If when you place an order and were given a promised delivery date, a buyer could deal with that.
The are so many scale jets out there with so many options that the companies producing the kits could not possibly plan ahead on what to produce. You get one buyer come along and want a bare bones kit and the next comes along and want a full blown kit with all the goodies.