All US customary units are defined by their metric equivalence ... so in one sense, the US uses metric for everything ...
The problem isn't the metric system itself ... it's the combination of metric and a decimalized currency ... In Europe, it's fairly easy to calculate the best deal, 500 grams at €10.00 is better than 250 grams at €7.50 ... most folks can do that in their head ...
The USA uses fractional measure and a decimalized currency ... near impossible to figure the best deal even with a handheld calculator ... 3 lbs, 2 oz at $6.00 "looks like" a better deal than 1 lbs 14 oz at $3.00 ... most folks would think they're getting 3 times the product for half the price ... ha ha ha ha ha ... the US system is specifically designed to increase profit margins ...
Also worth noting that all countries that use the metric system exclusively do so under penalty of law ... you'd get fined in England trying to sell 15 ells of rope for 4 guinea, 17 shilling and 8 pence ... whereas in the USA it's perfectly legal to sell apples by the peck ... as long as each peck is 8.81 liters ...