"I guess the general US public can't really grasp small fractional sizes or thousands?"

The fractional sizes would get weirded and weirder as they get smaller.

1mm is ~1/32 (5/128ths is a really close approximation, but let's assume nobody is that crazy).

Right now it's ~1/4 of an inch Let's say they reduce the size 1mm.

Now which sounds better: 5.1mm, or 7/32 of an inch (or 13/64ths, which is more accurate)