Its 20,000:1 based on the old peso, because in 1993 the peso did what was in effect a 1,000:1 reverse split where 1,000 old pesos (1,000 MXP) were exchanged for 1 new peso (1 MXN).
if you see a 40 year period, inflation is 200k%? (wow)
From what I have heard was happening in my home country as well during hyperinflation, usually you don't have access to the foreign currencies, only the politically connected people to. Then they dump the forex into the black currency market at ridiculously inflated prices
It's a lot easier for a poor person to find someone that will give them a dollar for their pesos than some satoshis...