There's more nuance to it though: if you take a closer look at fields where inch are used even in fully metric language environments you'll find that it's often more a class designation than a measurement. A 21 foot container does not exist (turns out that according to the wiki 20 foot containers aren't even allowed to be 20 foot long, they are 40/2 minus some defined amount of padding)

It's even more pronounced with camera sensors, the size given in fractions of an inch is some kind of "equivalent to", whereas the size in mm is the actual size. Apparently the image sensor inch is 16mm or something like that.