I think it’s a couple things with them… at one time, they were the (or almost the) most popular sort of figure Windstone produced. I think I remember Melody saying that once, and wizards in general were hot 30+/- years ago. So there were a lot produced, and wizards aren’t so popular anymore. Plus, the people who would have bought them all those years ago and maybe treasured them since, are getting older now. Many may be starting to downsize their possessions, or even sadly passing, and their family just aren’t interested in wizards.
The human wizards are pretty common on the secondhand market- even more so than the dinosaurs (don’t see near as many of those as you’d expect) and peacock dragons (maybe). The animal wizards are much harder to find secondhand and seem to hold their value better. Just my observations and thoughts.