@garry
Two possibilities:
- I suspect because it's scaleless, in human terms. What does it mean to say it's three times bigger? So it's not intuitive to think of it in that way.
- People buy online. They never hear the actual word.
Also, when you deal with binoculars (which is my referent in optics), you look at a set which are 8x42, and that's not a multiplication; it shows magnification and diameter of the lens. The useful thing is to divide not multiply. So the convention is unhelpful.