~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.
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.