I'll give it a guess. Knots is an excepted International Standard Measurement of speed and distance standardizing navigation maps and charts between nations. It lessens confusion in that respect. I think we are the only nation to use miles as a distance measurement in civilian terms. Knots and nautical is a maritime term.
The statute mile is used by the United Kingdom and many of its offspring including the USA.
The following was taken from www.dictionary.com...
nautical mile: A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet). Also called sea mile.
statute mile: a unit of length used in navigation; equivalent to the distance spanned by one second of arc in latitude; 1,852 meters
international nautical mile: a unit of length used in navigation; equivalent to the distance spanned by one second of arc in latitude; 1,852 meters.
air mile: A unit of distance in air travel, equal to one international nautical mile (6,076.115 feet).