That's because the original micro lenses were commissioned to resolve images of microfilms iirc[1] (See under 1962), and doesn't really have anything to do with the macro/micro relationship.
The name Macro makes perfect sense. It doesn’t refer to the size of the subjects being shot, but rather to the magnification factor. Macro lenses are capable of preserving 1:1 scale between the subject and film/sensor
There is a well understood difference between macroscopy and microscopy. Naming macro lenses micro might be helpful to the layperson but not the subject expert.
[1] - https://www.nikon.com/about/corporate/history/chronology/194...