Some of that is the weather and the economy, (which some media say is getting better, but folks down here in the real world aren't seeing it) and some of that is the format. Craigslist isn't as friendly or popular now as others sites, like FB marketplace. We've had a thread HERE about CL's nightmares since 2013...
face book has that deal where all they have 2 do is hit is it available,gerts real anoying,90% never follow up,if its still listed for sale it must be for sale ,i have it listed in my add,if its listed its still f"available"inquieres without contact info will not get a respones
Where I am, in San Francisco, there are a lot of ChiCom stylish bikes available new- things like Linus, Mission Bikes, Public Bikes, etc. That seems to have taken the bottom out of the older rebuilt bike market. Apart from the retro grouch folks, hipsters want what they are familiar with. For decades I've had no trouble flipping English Racers, now they just sit .
I have sold maybe 4 bikes and bought 2 off of FB marketplace. Also have had some success on CL. Looks to me that most people want a nice looking bike. 3 bikes were purchased cheap at a bike auction, had nice paint and chrome, but needed repairs such as rear wheel replaced or rear derailleur threads ripped out of the frame.
2 were cheap mountain bikes from Mallwart - sold fast this Summer for 1/2 of new $. One was 1980s vintage Huffy 3speed girls bike with nice full fenders and a basket got $150 with like new tires and tubes from another junk huffy. Last bike was my wife's Trek navagator, Which we sold for exactly what we paid a LBS for a clean used Giant hybrid that fits her better. Nice pictures and shiny paint brings them in to buy.