If everyone is passively investing, that no longer works. Then it's not even a market. We don't even know, for sure, if that works.
~62% of US adults own stocks: https://news.gallup.com/poll/266807/percentage-americans-own...
Isn't that very little money?
1 in 5 have $0
50% have enough to cover 3 months of expenses
You're saying that $500-600 (the amount you claim 50% of people have saved up, if it's the median) covers 3 months of expenses?
Yes, there are people who don't invest. Where do they keep their retirement savings? 40-50% of Americans, at least, simply have no retirement savings! Most people in America aren't earning enough to put away a meaningful amount for retirement. It's going to be grim as boomers and millennials hit retirement age and have to keep working.