...Why some few in the world resist the use of SI units is a mystery to me...

Just 'cos Napoleon went mad there's no reason for us to copy him.

And when you are talking about weight, the SI system doesn't have UNITS it has A UNIT which is why it is so useless. A system of units has to have more than one unit. Most systems of units have grown up over hundreds of years and each step has been chosen for its utility for a specific application. The gram however was chosen by a madmans scientists to create confusion amongst his conquered nations, in the same way that he chose to drive on the wrong side of the road.