Anyone who's ever done an international relocation understands this. It works like this.
Your company asks you, a SF-based tech executive, to relocate to India for a three-year assignment.
Notional cost of living in India is absurdly low. But your company will actually estimate that you'll need ~$50-100,000 more per year from a COL perspective.
This is because your existing lifestyle is now composed of what are all luxury goods in India.
A Toyota Camry is an expensive, luxury car in India with massively high rates of taxation. Even if you don't currently own a car, you will need to, because public transportation is some combination of unreliable, unsafe or unavailable. Vehicle maintenance will be much more expensive and frequent due to poor roads and the frequency of fender-benders.
Your company will tell you that they recommend in the strongest possible terms that you hire a driver from the local area, because of the track record of outcomes when an expat gets into a traffic accident.
Alcohol is incredibly expensive, particularly imported brands. Good luck if you like to eat steak. Restaurants that serve international cuisine are relatively rare, and those of good quality are actually expensive even by international standards. If you want to buy an item of technology that's near the leading edge, it's either not available, or only available via import with massive surcharges and taxes.
Very little of the housing stock will meet your expectations, and you will probably end up in one of a very-few 'expat friendly' areas. You will be buying bottled water because the domestic water is not safe to drink. If you want to be confident of 24 hour power, you will either end up needing a place with its own generator, or to be in the one of the super-elite compounds that provides its own generation capacity where you're literally paying major world city prices.
Visiting your family is now international travel involving stop-overs in Doha or London. Facilitation payments/bribes are now a budget item.
The point is: cost of living differs depending on expectation. If you go to Mexico to live like a local, it will be very cheap. If you go to Mexico to live like an American, it will not be.
EDIT: in fact, the real surprise to me was that the COL data from the big relo vendors like Cartus is nothing like symmetrical. If you look at say London/Tokyo as a city pair - there's a fairly large COL increase for moves in either direction.