and don't learn anything at school

That's not true! They learn how to hide under desks

You didn't learn active shooter drills? How did you avoid getting shot?

So the most American things in America are using the least American measurement system?

It's a pretty heavy mix, many of the most popular rounds are also referenced by their metric size but they're not usually 'useful' sizes in either standard or metric.

For example:

• .22 LR = .223in = 5.56 NATO
• 9mm = .357 mag
• .40 S&W = 10mm Auto
• .308 = 7.62mm
• .44 = no common metric eq.
• .45 = no common metric eq.
• .50 = 12.7mm

no one gives a measurement as 1 mile 300 yards 2 feet 6 inches.

When this topic came up yet another time previously, USian engineers proudly chimed in saying that their software accepts any kinds of units and converts between them as needed, so they put in US units without bothering about whether metric units are used elsewhere in the project. Ergo, someone does in fact give measurements like in your example.