One US Dollar equals NINETEEN Pesos today. If that was reversed?? $20 = One Peso? Millions of Americans would be flooding into Mexico illegally for the money. Arbitrage they call it.
Chinese Yuan? $1 = 6.45 Yuan. If THAT was reversed?? The USA would be exporting to China. And China would be creating fake unneeded jobs at other Chinese people expense.
Before WW II $1 = 1 Yen, after WW II they made $1 = 360 Yen.