My best guess is their position in the food chain and the resources in the local population.. Why do you ask? 😁😁
Discussion
Many cultures have and continue to use shells as currency.
They are collected from nature, not controlled by any government or bank.
My point is that decentralised currency is not new.
It's actually the default.
I know I know... I was just joking around.. Your point is well received..
I would've replied similarly if it's about gold "geology, volcanoes, extraction and refinement technology something something..."