I've spent a significant part of my life in sales. Yet, I'm still surprised that people just don't seem to get it -- no matter how long -- that it is price. If your item isn't selling then it's overpriced.
I've spent enough time in sales to have had the following drilled into me -- ad nauseum -- a market transaction is when BOTH seller and buyer have come to a MUTUAL agreement on price and terms.
I perused some of the responses to the OP, which include shrinking buyer pool, less interest in the hobby, etc. This also considers the responses related to time of year, etc. This is ALL on the demand side of the equation. So, if your item isn't selling what does that tell you about the demand side of the equation?