Because Americans don't "save" their money in traditional savings accounts anymore. They shove it in investment accounts of varying types (less common) or retirement accounts (more common). When there's an emergency we tend to put it on credit and then use the time that buys to get money out of one of those other accounts and pay down the balance. Even many people who are living paycheck to paycheck are making some sort of 401k contribution which, while not a proper "savings" slush fund, can serve the same purpose of being able to cover an emergency expense if needed.
Americans definitely keep emergency cash in savings accounts or at the worst, money market accounts. I doubt "Americans" as a generalized entity even have investment accounts, outside of whatever tax advantaged account employer offers.
By and large, "Americans" probably just don't have sufficient cash flow to create a decent emergency fund, and/or they lack the discipline.
I would hope that higher earners and higher educated are trying to keep at least 6 months of highly liquid assets available, i.e. cash in savings accounts or money market funds.
