It doesn't make sense from a practical standpoint — but then, the reason 'Murricans still use Imperial weights and measures has nothing to do with practicality and everything to do with emotional symbolism.
By pig-headedly sticking to Imperial units, and forcing all the companies that want to sell their products both in central North America and the Free(r) World to spend Saganesque billions of dollars in redundancy (labelling, packaging, inventory management and so on), 'Murricans are doing their considerable best to ensure that their products have a hard time being sold outside their borders, accelerating the out-of-control trade imbalance and hastening the demise of what once was the United States of America as a meaningful player in world trade. Maybe when world trade moves away from the US dollar as the global reserve currency, people will finally begin to understand how badly they've been screwed and why; my guess is they'll keep on lapping up the corporate propaganda that's replaced American news reporting and continue to blame every imaginable outside influence that scapegoats them having to take actual responsibility for and control of what in living memory was our country.
Things are going to keep accelerating downhill, and this is a poster-child-level reason for "why".
Paris for her corporately-groomed, information-free symbolism of what's wrong with America.