Jim Weisgram wrote:
But what seems to be the reason for the US hold-out to stay with an
archaic system?

Well, I think it is pretty complicated stuff to move from Imperial to metric.

The easiest way would be to repeal the laws that forbid voluntary full
metrication and trade in metric only products.

For example, the FPLA is a Federal law covers packaged goods that you
see in the supermarket. It mandates non-metric units on the label. A
two liter bottle with a label that says "2 L" is legal in all
countries except the USA. There is a proposal to change the FPLA. Many
manufacturers want the freedom to offer metric-only labels (as you can
see with wine and liquor) and don't want to pay the costs of
relabeling just for the US.

Many Americans are unaware that non-metric units are mandatory.