I've even seen this with scooters. The sweet spot for a model I'm interested in is probably $800-$950, and those sell within days. Others for $1250-up don't move. I've seen one listed for nearly a year now. $1800. Dude relists it on CL three times a week. It's the oldest model year for the scooter also. (For another $400, I can buy one brand new, 15 years newer.) The sweet spot for pricing pretty much aligns with the "blue book" price for these items.
Not saying it's always the case, but there are too many sellers for just about anything these days who think these high prices will eventually work. And they get too insulted if the reasonable offer isn't close to asking price, even if a current market value (based on recent sales) is the offer.
Some buyers are no better. The worst are on CL. They low-ball just because they can. I had some dink argue with me that the Rotel I was selling was way overpriced. As his proof, he pointed to an eBay listing for a lower powered version that was beat to snot. Typical of the CL mindset.
Another thing ruining sales for sellers is eBay's "buyer is always right" policy. Buyer's remorse plays into a lot of it. They'll claim some false defect to return it. Others will damage an item and file a claim saying the item was not as described. With vintage items, I've heard of fellow hobbyists sending out a restored amp or receiver, then find the buyer has swapped out good parts for bad, filing a "not as described" claim. Sellers are getting screwed on eBay (and Amazon), which is why many of us are now gun shy to sell any of our equipment online.
Many forces are tugging against each other, which I feel are all detrimental to the drop in activity at all of the buy/sell sites these days.