this has been discussed on several occasions, but I will revisit.
With the passing of Rhett Stidham and the demise of the RKS, collectors are no longer getting the exposure to the knife collecting hobby in general, and of course RMK's.
Rhett traveled across the country all year long doing shows from California, Oregon, Texas, Vegas, Tennessee, Oklahoma, New York, Georgia, Florida, etc. He always had his ubiquitous RKS sign on his table, was willing to talk to folks, and promoted the hobby every day.
He was regular with the newsletter 4 times a year. He would always get a few recruits at a show. He was the consumate promotor. That is how he made his living so he had a vested interest in keeping interest high.
That is the biggest reason in my opinion and of course the economy comes into play also. Collectibles of many items have fallen out, but if folks aren't getting educated and and there is little promotion of the hobby other than internet sites, you have what you have. As of yet, no one has filled Rhett's shoes.
If you make a living off knives, and you want the hobby to grow, there is no substitute with putting a face to it.