It's always an ebb and flow. The demand for muscle cars you used as an example has been affected in multiple ways, much like the knife market. It was insanely inflated during the late 90's and early 2000's, before the crash, and it certainly suffered a set back but it's far from a dead market (well maybe muscle cars, but not classic cars in general). Of course, it changes with the times also. Models that were less sought after have become more so, and things like vintage trucks and SUVs are making a huge showing. The market for old Jeep Wagoneers and J-trucks has gotten insane compared to it's relative non-existance a handful of years ago, but there's more of a trend toward doing modern engine swaps with higher efficiency, than building the old V8's to high power potential.
Diesel swaps in all types of vintage cars are common place now, when they used to be pretty rare from my perspective.
My point to all this is, it's normal for markets to evolve. Anything that reaches huge popularity levels, is bound to fall off, or re-orient. It's been pretty apparent with all trends, and I'm sure we all have seen which types of knives have peaked in the past decade. On the other hand, from my perspective, other types of knives, like fine slipjoints, seem to be enjoying renewed enthusiasm. Or maybe that's just what I tell myself since that's mostly what I'm interested in making anymore.
It's an interesting subject to consider, I remember 5 or 6 years ago where every conversation I'd have with another maker would eventually end up with "we need to start making more kitchen knives" etc., but that area feels pretty saturated to me now, and I'm glad I didn't move into it. I make a few, but mostly for fun. On the other hand, the tactical folder market, which I believe was hugely oversaturated, is bringing new people to the fine folder market, as their tastes evolve.
