I'm sure part of the reason is that it's just a snap shot in time.
Maybe another part of the reason you see fewer Kirkhams for sale is because at $100,000 for a roller and probably another $50,000 +/- to finish (options, polishing/paint, engine, trans, blah, blah, blah), many owners (no, not all) have a higher disposable income and can afford to keep their toys longer and still buy other "objects of their affection" aka "The Jay Leno Effect."
And buying, selling and trading at $50,000 +/- is a helluva lot easier than 3x that amount. The SPF is also a great well-known brand within our community and I'm sure a good chunk of their buyer profile are 1st time Cobra owners, who want a solid well-built well-known brand of Cobra replica, try it out for a while, and often decide they don't like Cobras, which inevitably leads to their selling it.
Pure speculation.
