Because people don't want to? After all, Ghod forbid that they should
choose.

I choose metric, as do a large proportion of my generation. I find that my
generation uses metric for everything, except the following:

1. Road distances and speeds
2. Volume of beer and cider (but not other drinks)
3. Weight of a person only (but not other things)
4. Height of a person only (but not other things)
5. Idioms

Christian.