Because the rest of the world is metric and they sell their chips there more than here I’m guessing.
Hard to imagine they sell more of these outside the US although I'm sure Canadians buy their share.
Maybe cause of this: Garmin Ltd. is an American multinational technology company founded in 1989 by Gary Burrell and Min Kao in Lenexa, Kansas, United States, with headquarters in Olathe, Kansas. Since 2010, the company is incorporated in Schaffhausen, Switzerland.
Another US co. gone GLOBAL.