https://en.wikipedia.org/wiki/List_of_FIFA_country_codes
It is their official FIFA 3 letter designation, I'm not sure exactly why.
This is what Google's AI says
"This abbreviation comes from the French name for the country, Maroc. While "MOR" might seem more intuitive for English speakers, FIFA historically assigns codes based on the country's French moniker due to the nation's colonial history and French language influence."