People are realizing that some of the Lampropeltis have been very underrated for some time, and are changing demand. The value of mountain kings, grey bands, and black milks has doubled/tripled or more during that time frame too.
There doesn't have to be some 'event' for values to vary over the course of more than a decade. Anyway, these are probably best considered Veblen goods, and as such don't follow supply/demand expectations.
https://en.wikipedia.org/wiki/Veblen_good