There's a difference between accuracy and precision, and there's also a difference between consistency and convenience.
It's the reason I might choose Ruby over C (convenience - Ruby was designed to be centred around the human, like many Imperial measures, and non-decimal currency btw), or use feet instead of metres (because I have feet that are, astonishingly, close to a foot long) or any other number of examples where metric is not the best or a better choice.
I'll leave you to divide 100 by 3 or 12 so I can buy 1 or 4 of those dozen eggs you're selling with £1 while this Victorian street urchin who's had little to no schooling beats you at it because they're using a non-decimal currency with more factors…
tl;dr People in the past weren't stupid, they just had less access to the technology required to maintain a metric or decimal system in a widespread number of contexts. The existence of such technology does not obviate their usefulness.
It's the reason I might choose Ruby over C (convenience - Ruby was designed to be centred around the human, like many Imperial measures, and non-decimal currency btw), or use feet instead of metres (because I have feet that are, astonishingly, close to a foot long) or any other number of examples where metric is not the best or a better choice.
I'll leave you to divide 100 by 3 or 12 so I can buy 1 or 4 of those dozen eggs you're selling with £1 while this Victorian street urchin who's had little to no schooling beats you at it because they're using a non-decimal currency with more factors…
tl;dr People in the past weren't stupid, they just had less access to the technology required to maintain a metric or decimal system in a widespread number of contexts. The existence of such technology does not obviate their usefulness.