I've never met a person with adhd in my entire life. Why is it so widespread in the US?
If you look at most countries besides the US, there is a distinct "slacker" subculture that is likely a bunch of people with undiagnosed ADHD. NEETs in Japan, for example. These are approached as unique cultural phenomena, rather than through the lens of epidemiology.
(Other thought: maybe you have met someone diagnosed with ADHD, but they've never told you they have it. I don't go around telling my friends and coworkers I have ADHD; it's an annoying conversation to have with someone if you don't know whether they know enough about the disease to separate it from "laziness" as a temporary emotion. I just blab about it to strangers on the internet.)