I'm of the opinion there just isn't as much dispensable income as there has been the last couple of years for most people, so items like clarinets are taking a back seat to where they are spending their money right now. I also think the people with the dispensable income also have other things going on like "work" which doesn't allow them as much time to go through for sale listings. I know the later affects me a lot of the time, I miss out on a lot of the bargain clarinets, because I don't look through the listing like I do when I have time. When I do have time I do tend to make more offers or bids on instruments, and yes some of them have been listed for a while, or were listed previously and didn't sell and I contact the seller, some of these as much as a month after their listing ended. These usually end up being a purchase.
I don't get too worried when listed items don't sell, I just assume a lot of other people are like me, when you have the time you will look, find it and make a purchase then. It would probably be different if it was a sale of necessity, but everything I list is usually something that can sit around for a while if it needs to and wait for the right set of eyes to see it, eventually those eyes will see it and it gets sold.