Because Americans have the mentality of running things. Kinda like when the rest of the world uses the metric system and America goes "Fuck that, we're using English".

I wish the US would stick with the UN. People are saying that we usually have to pay the costs for the UN, but we end up paying them anyways. We might as well pay and have international backing at the same time.

Regarding the metric system, The main reason I understand for not adopting it, is that the cost would be prohibitive.

Even if we phased it in slowly, heavy machinery, screw threads, and a bunch of other shit would still be a huge problem and it would take a LONG ass time and a bunch of money to make it official.

The way I see it, It's not too hard to use conversions. If there are 2.2lbs in a kg. Then it's easy enough to use the quick multiply by 11 rule and then multiply by two. So for 52kg it's easy to say that 5 + 2 = 7 so 52*11 = 572 or 52 * 1.1 = 57.2 and 57.2 * 2 = 114.4. So 52kg = about 114 lbs.

For feet to meters, there are a few simple and fast conversions that aren't of great precision, but accurate enough for me. For example, 3m = 10ft, 1 in. = 2.54cm, 1m = 40in. Of course for precision, I would alway use a calculator...

Regarding volume. For a fast calculation, you can simply relate the liter to the quart since when it comes to serving drinks, there's not a great deal of difference. When I need precision, it's easy to remember the numbers I've seen on American Coke bottles my entire life. A 2 liter bottle always says 67.6 fluid ounces on it. This is my base point for conversion since I can gather that 33.8 fl oz is 1 liter.

For temperature, that's a no brainer. 0c is freezing, 100c is boiling. 32F is freezing, 212F is boiling. So 212 - 32 = 180 and 100 - 0 = 100. Therefore it's easy to assume that 180/100 is the ratio. That easily converts to 9/5. Be sure to compensate for the 32 degree shift on the Fahrenheit side.

So what it comes down to is that if you can get through school in any country without understanding that both systems are just really simple. If you don't get it, then go back to school and work on it. If you can remember there's 12 inches in a foot and 8 oz in a cup, then you can remember 3 points of conversion reference and derive the rest.