Because they don’t realize that nothing is worth any more than what someone is willing to pay for it.
Secondly, most of these people weren’t buying, and selling, gear on Audiogon since it’s inception. Therefore they don’t have a clue what gear is worth. Don’t mind me, I’m an old dog. How many here actually bought used gear on rec.audio.marketplace? Those were the days in the early 90’s, long before AG existed. Who remembers AudioWeb Classifieds? Remember when Audio Review had the biggest used gear marketplace on the internet?