Why do many Americans see moving out at 18 as a sign of maturity rather than just a financial choice?

In many cultures, living with your parents into your 20s is totally normal, even expected.

But in the U.S., people often treat moving out at 18 as a sign of being a “real adult.”

I’ve always wondered — why is independence so strongly tied to leaving home, even when the economic reality doesn’t make it practical anymore?

Is it cultural pride, social pressure, or something deeper about how Americans define adulthood?