I believe it ties a lot to the fickle nature of the audiophile market. I personally have a REF75SE, sold it, missed it terribly, and went to buy a replacement as soon as one became available. From the audiogon listing to sale lasted less than 1 day. Of course, pricing things realistically (thank you audiogon blue book) makes a big difference. So if you have buyer waiting for something to hit the market, a sale can be very quick. If not (especially given the price of a lot of the gear here plus some economic uncertainty) than things can sit. And sit. And sit.
what does amaze me is when something sits for quite a while and seller won’t budge on price. Somewhere many moons ago I read something about “supply and demand.”