Because, just because.  Air, airports and foreign AND domestic gateways.

My Airfare Service Tip of the Day 1 is below 

Tip: 
For international roundtrip flights, connection times are very important, even on domestic layovers, because the majority of airports do not drop a passenger off in the same terminal your international flight is departing from. This means they will have to hoof it to their gate. (i.e., Amsterdam, Heathrow, DeGaulle, etc)  (Seattle, Los Angeles, San Francisco, Miami, etc)

If you have an international connection, leaving more time is even more cruicial. 

Appropriate Outbound connection times: 
US Connection: no less than 80 minutes
Europe Connection : no less than 2 hours but ideally 2.5-3 hours if available 

Inbound to the USA or a CBP airport like Dublin (assuming no Global Entry): 3-5 hours especially if the airport is difficult or the domestic terminal is far away from the international terminal.

Please be aware that when you are out and about -- no us currency accepted you must pay in pesos.  This is true and not something new.  You cannot pay for goods and services with USD $$.

However, you can pay by credit card, but not USD cash.  So, before you go, be sure and get some pesos to have on hand if you don't want to pay for every little thing by credit card, i.e., a beer and chips or tacos.

Check with your bank for foreign money or there are places where you can get pesos - AAA or a bank but it does take awhile, so plan ahead.  You MAY be able to exchange money at the  hotel or resort where you are staying.