Because it's kind of a specialty product, not made in large quantities, not in current production, and it's not really all that outdated.
When a company stops producing premium hardware, the price tends to rise for a little while, because people who have systems built around those parts will pay more than MSRP to not have to replace their entire system.
You will tend to see a similar thing happen with consumer-level parts when a new socket comes out, although it's not as extreme - once all the liquidation sales sell out, you'll see particularly desirable New-Old-Stock LGA1150 CPUs and Motherboards (enthusiast-class kit, -K CPUs and high end mobos) selling for a the same price as equivalent LGA1151 parts, if not a few bucks more.