Many of those people living paycheck to paycheck have a budget where they're saving or investing a significant amount of their money, and accordingly, money feels tight. This is the financially sound way to avoid lifestyle creep, but it doesn't mean you're in a precarious position. Or alternatively, they're paying for really expensive, but optional things like private schooling and expensive cars or vacations.
Obviously some people are struggling, but this paycheck-to-paycheck stat is not an accurate way to quantify that. It's best IMO to look at objective metrics like the poverty rate, or people's objective financial picture (available via surveys.)