Ok, 21% directly own stocks, but this figure was since 2022. It could be more today.
Anyway, even those who own via 401k (which is up to 58%), would also be affected as the value of their 401k will dip when the market dips as well. This is especially critical to those above 60 who may want to start making their withdrawals to complement their retirement expenses. Even if they have the holding power, it may take a few years to fully recover, and this is also not a guarantee, pending on the fund managers' choice of stocks. Those invested via mutual funds would be even more affected since their redemption is not restricted by age.