I am with you. The catalytic converter argument seemed to explain the run up in price when palladium cost less than platinum, but once palladium got more expensive, that reason stopped making sense to me.
What else is palladium good for? Coins? No way the US Mint decision to make a palladium offering caused that big of a price swing. Right?
That is logical, but seems the auto makers would have shifted back to platinum once palladium doubled the price of platinum. That was the stated reason 5 year’s ago for the move to palladium to start with - that platinum was too expensive and palladium was almost as good, but at half the price.
From what I've read/heard, one of the major reasons palladium and rhodium prices have been rising in recent years has been supply shortage. Not sure that usage has been increasing... may have been. But with stable usage and contracting supply, prices normally rise.