Do people really just not get it that their items are not selling...

What Music Room sells appears to be mostly overpriced, sure.
My impression regarding haves and have-nots among those who participate is mixed and complicated. Besides, I think that some are just not in the mood to buy for various reasons. But that's active participants. Perhaps many sales go overseas especially to Asia. I also see some good 220V equipment from overseas dealers that no-one buys for months, some priced reasonably but still quite expensive. But you are right, $2k for old piece is already a lot of money, certainly for me.
Overall things don't go well, no doubt.

I urge all sellers to overprice everything and hold it like that. There will be a lot of buyers, just wait for couple of months. That's how you capture the market and inflate the value while creating new normal. Prices are often already inflated. Ten year old piece, whatever it is, with some exception, should cost no more than 10% of its new equivalent. 
When item is priced low and sold very fast, this creates unfair situation when most members can't even see the ad let alone have time to think of whether or not buy it. First come first 'steal', right ? Right. 

So they do it intentionally, it is just a different and opposite intention.

To be able to successfully negotiate, besides knowledge and intellect, you need to acknowledge and understand the other side, another person. Not easy or simple.
Determining fair price is often interesting. In the past, couple of times I refused sellers' offers but not because I thought they were unfair, it just was too much for me at that moment. And I told them so, including that I thought their offers were indeed fair.

On the other hand, the other day I was talking to a Japanese record seller on discogs. The record was advertised as NM, so I just asked him to confirm the condition. He play graded it and said no, it has some noise in couple of places, though it does look NM. Then he corrected his add and lowered the price. Nice. We'll see, I bought it, should be very strong VG+ - acceptable.

But the funniest things I saw were on ebay, some Russian and Japanese sellers really look for idiots, they might themselves be idiots as well. I mean both equipment and records.

Rare items in high demand is a separate category.

Yeah, your beloved used equipment is worth exactly d*ck until someone wants to give you money for it.
I did notice that some asking prices for cables look ridiculous, at least to me. Who pays more than 50% retail for used cables ? Especially expensive cables. Not I, that's for sure.