“Americans” is a stupidly large and diverse population to say anything meaningful about. It’s extremely unlikely that that any population of humans of such a size doesn’t include some individuals who are more extreme than you, both more and less, for almost all traits.

You’re less likely to observe introverts than extroverts because one of those types will tend to do things in a way that are less likely to get your attention. You’re might well be experiencing observation/selection bias, possibly also reinforced by confirmation bias.

But whatever you think to be the “typical”, even if you could estimate it using some unbiased sampling method, it is often not a helpful way describe the whole population, or at best a reductive “average” that has limited useful applications.

TLDR - human populations are diverse. I don’t think any nation has ever effectively brainwashed or eugenicised their population into a single homogeneous group.