I just dont get it either, I too had made a reasonable offer on a desert storm gun in the past and it was denied - the person never sold it. I have more rare, and lesser known glocks in my collection that I have gotten for a steal out of peoples ignorance. I think in general people are just being greedy and not getting the right info about market values. Just because some auction a-hole says/thinks something is worth xxxx dollars does not make it true.
Maybe in a perfect setting, in a bidding war with two or more motivated buyers, prices can go up - but that is not trypical and representing a market as a whole.
Here is a pic of my favorite ultra rare Glock, most people in the US dont even know these exist. The P9M is mostly jst a Glock 17 - A very, very small batch of these GSG 9 marine unit guns were imported. The guns came from the factory shipped to German BStU, with extra power red firing pin spring, marine cups, and lanyard for use in special operations in and around water.