It has to be platinum because they are exploiting a legal loophole. Ever seen those 1 oz gold or silver coins with a face value of 10 dollars despite the precious metals being worth much more than that? It's the same thing, just in reverse, only that they have regulations in place for gold and silver coins but none for platinum.

I always find it hilarious when they pretend to have forgotten that they can just print more money. The best was when the Treasury auctioned off confiscated Bitcoin - for dollars, which they could also print for free.

I guess their chief wizard failed to cast the correct spell by spilling some ink on the holy papyrus back at their financial temple of doom or something.