It's all relative. They sell far fewer than "other more ubiquitous wood working tools of similar quality and complexity". That is one factor. Actual cost is another. Sometimes you'd be surprised when you do an actual costing of the parts list. Each casting is low volume...
Consider also the cost to have a frame build for you versus building one yourself. In those terms, even buying the tools you come out ahead doing it your self. It's all relative. Average the tool cost over the whole life and usefulness of the tool. It may not seem so much in those terms. Looking at the cost versus doing only 1 frame, sure it seems more costly. It's all relative.
