I think that whoever it was that decided the States should switch from metric measurements to the "American System" really was thinking about the future generations. I think I can imagine what they were thinking. It really was genius.
If you've grown up in the States, learning the "American system" & maybe dabbling in the metric from time to time in math or science classes, you become accustomed to the "American System" for almost everything. If you know metric at all, it's most likely a separate thing, & almost no one knows how to do conversions between the two.
Occasionally an American might take it upon themselves to move out of the country & this is where the genius of the plan lies. You go to the grocery store to buy 2 pounds of beef. However, meat is sold by the kilogram. Perhaps you'd like to buy a gallon of milk, no dice, all liquids are sold by the litre. How about an 8 ounce can of tomato sauce? Sorry, millilitres only. If you're unfortunate enough to have a recipe box full of recipes from the States, you might as well throw them out b/c you'll never be able to figure out how much of anything you need to buy at the store. It might even be easier to just move back to the States. If you're a US citizen, they're making you file taxes there anyways, might as well move back & simplify things.
The plan was actually twofold. There's another side of it. Not only does it keep Americans IN the country, all the other countries use metric, so immigrants not only have a language barrier, they also have a metric barrier. Good luck finding your 250 grams of shrimp for your salad. Need a pint of milk for something? Better make sure you know if that's an American pint or a metric pint, because they are different!
It's enough to drive a person batty!