I think dalee has a bit of a handle on it. It's a combination of change in values of a society, as well as the harsh economics of marketing. It's going to be very hard to market a little traditional pocket knife with real bone handles for more money than a black zytel bead blasted knife that costs way less to produce. Lets face the music; we here on a traditional knife forums care about the asthetics of the thing, while most people who by some miricle do recognize they need a knife, will get the cheaper knife. They don't care if the handles are black plastic, or the blade is a stamped out tumbled finish thing, all they care about is will it cut?
It's like what is going on in the gun world. The parralel is close. Glocks and SIG's fly off the shelf as does anything with a black stock and stamped receiver. Not many shooters these days are going to high end rifles with hand cut checkering on Turkish walnut stocks. Of the gun shops in my area, there are none that have a selection of nice rifles or shotguns. But if I want an AK or AR, or even a SKS, well, there's plenty to choose from. The nice guns with the afor mentioned turkish walnut stocks are now a nitch market.
I think we're living in an age where style, beauty of design, all have been sacraficed on the alter of function. The old saying of form follows function has been tossed aside for just function. No asthetics. Why would one even want jigged bone handle's, let alone stag, when for less money one can have black synthetic that you can run over with a truck, throw against the side of a building, with little or no damage?
Our little family of folksy looks at an old knife and wonders what memories it holds, or love it for the past era it represents. The new kids on the block see it as an old relic from the past that has no value to them at all. Some are even mystified as to how the old geezers used a knife that (horror upon horror) didn't even have a blade lock, or need two hands to open.
I do think the slip joints are going to becone a nitch knife for two groups of people. The older guys, who like the guys who ride Harleys instead of crotch rockets, care about the style of the thing as well as having memories of a dad or graddad who used a similar knife. Or some younger guys who are lucky enough that they had a graddad or older mentor who used one. There may be some young guys who by accident of fate, get to use a traditional knife, and experiance the cutting ability, and versitility. For all of them, the companies like Case, Queen, GEC, will be the nitch marketers that keep them in traditional knives. But they will be the minority of the knife buying public, like the well heeled white collar people who buy a side by side Mercle shotgun with engraved receiver, rather than a tactical outfitted 870 with light bar under the extended magazine.
It's all about values, or the lack of, that drives the markets. The proffit must be increased, no matter what loss of asthetics.