Because the kind of American that understands that not everyone knows how big a foot is already puts the actual length in brackets so the people that cause prob

Because the kind of American that understands that not everyone knows how big a foot is already puts the actual length in brackets so the people that cause problems wouldn't use it even if it was a feature. Also, if it worked like <date> you'd have to put the value in a standardised unit (eg SI units) which would also annoy the Americans and they'd refuse to do it.