Here's why:
* Abbreviations are often used for states, countries, or airports. London is a city, not a state or country.
* Using just two letters can cause confusion. Many cities have names that start with "L" or "Lo" so it wouldn't be clear which London you were referring to.
Instead of using a 2-letter abbreviation, you can use:
* LON: This is the IATA code for London Heathrow Airport, which is often used as a shorthand for the city itself.
* LDN: This is a popular informal abbreviation for London.
* Simply write out "London". This is always the clearest and most unambiguous option.