It's all a personal thing and the final price for this stem does not neccessarily follow the logic of your typical C&V component for sale.
Sometimes when you feel like you just have to get something you just go and get it for as much as you can afford at that time. I'm sure that many of those bidders have also experienced the mistake of being reluctant when a similar opportunity presented itself and then never happened again for many years till now, like maybe another stem like this years ago......and they have been kicking themselves on the butt since then. Now they are trying not to do the same mistake again even if it take over 500 bucks to get it.....in short, the stem in that condition must be $500+ rare these days.
Ehhh......what's 500 bucks anyway. It's just the price of a kinda nice watch. Tha's what I told myself when I bought some personal "must have" expensive C&V components earlier this year.

Chombi