Honestly, I think because they can be somewhat hard to get and they carry the name Pamp which is Swiss made and very popular. I am not sure why The year of the Snake is so expensive but I would love to hear why from others if they know.
It’s all in the name….. hahaha Pamp is a reputable name in the precious metals minting world so guess that (lamely) justifies the premium that we pay for the perceived premium quality.
Pamp built it's brand to command a premium. OPM is sort of the opposite. The brand stands for low cost, generic, mass produced metals.