There is an "economic" explanation for the phenomenon under discussion. Knowing whether a used firearm is "worth it" requires knowledge that not all have. Those who have it expended time, energy, and probably $$$ -- all valuable economically -- acquiring it. When the economic value of that knowledge and skill is factored in, and added to the cost of used firearms, it might even exceed the cost of a new one. Those that don't have this skill and knowledge face three choices: (1) trust the opinion of someone who does have the knowledge, if they have access to such a person, (2) buy in ignorance, and hope for the best, or (3) buy a new firearm, where the uncertainties are less, and usually covered by warranty. The latter is a perfectly rational response under the circumstances.
All of my handguns were purchased new, for just this reason. I'm a shooter, not a gunsmith, collector or one who otherwise imagines himself skilled in assessing whether used firearms are "worth it." Several of my rifles are used, but it is typically difficult to purchase milsurps in any other condition.
Like some, I've purchased used firearms where what I wanted was not available new, and I just hoped for the best. I picked up a pre-cross bolt safety Marlin 1894C .357 at a gun show a few years ago. But ignoring the milsurps, I tend to purchase my rifles new, rather than used, for the reason stated above. These range from a Ruger 10-22, purchased almost 40 years ago, to my newest rifle, a Ruger GSR bought NIB at a gun show last December.
Does that answer the question?