One major thing is that demographics are shifting. What was popular is not as popular today. Guys in their forties want the cars (and trucks) they lusted after in their teens.
This is what guys my age liked when I was in my teens
https://www.barrett-jackson.com/Events/Event/Details/1972-CHEVROLET-K5-BLAZER-CUSTOM-SUV-236127 Sold for 137,500
That's good money for that truck. It's where the market is going.
Japanese stuff is starting to pickup. Again guys my age wanted this stuff but couldn't afford it.
https://www.barrett-jackson.com/Events/Event/Details/1987-TOYOTA-SUPRA-TURBO-TARGA-236294 Sold for $71,500
https://www.barrett-jackson.com/Events/Event/Details/1993-TOYOTA-SUPRA-TURBO-LIFTBACK-237705 Sold for $104,500
Studying various auction results one thing I've noticed is that if you have something that's popular, or special and done right it will bring the money. If it's not or it's kinda run of the mill it won't. There is a lot of shiny crap run through at BJ and Mecum. RM, Gooding, Bonham's are much more picky about what they auction.
Example
https://www.barrett-jackson.com/Events/Event/Details/1949-CHEVROLET-3100-CUSTOM-PICKUP-237028 Sold for $176,000
You could have made good money doing that truck.
Case in point (for the won't)
https://www.barrett-jackson.com/Events/Event/Details/1955-GMC-100-CUSTOM-PICKUP-236992 Sold for $59400
On paper that truck should have brought 6 figures, Gold Star for someone to point out why it didn't.