Greed...good old fashioned greed. Probably a bit of pig-headedness too. A person will see a magazine being offered for say $180 and thinks, "That's what it's 'going for.'"
It's not 'going for' that much, it's just what someone is asking. They don't follow it and see what it sells for, if it sells at all. They get it in their head that this is what it's worth and that figure sticks. Every month or two the seller will drop the price a few bucks but of course it makes no difference. I mentioned this to Ebay but of course they won't listen to me, while in the same breath they complain that sales are waaaaay down. They need to bring back listing fees. I also watch car parts for my vintage car and see the same problem. The smart sellers listing for low prices, get a bunch of people into a bidding war and wind up selling while the greedy so-n-so's watch their items sit there for months.