Because it's a perfectly valid system of measurement. When I'm machining stuff I routinely use both imperial and metric systems (though not on the same job, one or the other at a time), as both have pluses and minuses. But as the actual numbers used are, ultimately, arbitrary lengths that someone, somewhere decided as defacto.
I'm even more inclinded to use imperial units in everyday life as the short sighted, pompous, idiotic and stupid EU beaurocrats have 'banned' it's use for the vast majority of applications. As soon as anything is needlessly banned I try and use it. I do and say a lot of things that are banned, often BECAUSE they are banned. Don't let the EU create an Orwellian society. 1984 this ain't.