Weights and measures for sale, which are the metric examples you quote, were forced on people by law. They were never adopted with any enthusiasm. People use the old imperial measures among themselves, although mm and g come in useful for small things (thou, 32nds and drams are a bit esoteric).
SI units make sense for science. I did an engineering degree and the American units are horrific. They taught us a bit of that stuff to show us how to appreciate SI.
Btw, I was only taught metric at school (cgs) and I was vehemently opposed to Brexit. But imperial units make sense for everyday purposes as they are the right size, arrived at by custom and long use.