Of that 50%, many have negative wealth due to eg credit card debt, many have zero wealth because they're poor, and many have all of their wealth tied up in houses or cars. It's probably not ignorance so much as lack of savings to invest.

You could buy a cheaper car, or a cheaper house, or cheaper clothes, and put the difference into an IRA.

Yes some people must spend all their income on food and shelter. And government assistance stupidly penalizes people who try to save. But many people, even lower income people, could save a little. I think they have never been shown what the power of compounding can do over time. It is not intuitive, because the gains in early years are small.

It's not really a matter of education, I'm in the bottom 50% and after rent and bills I'm left with very little. It's a highly competitive system, with winners and losers.

Wouldn’t something like requiring their employers to pay into a pension fund that is invested in a safe mix of stocks and other assets allow more of the population to share in corporate profits? (Ignoring social security for the moment, but assuming the policy was implemented as a similar sort of thing; but perhaps not as a deduction from the nominal wage).

I don't think that's a good assumption. What you know is that, at the moment, some kinds of owning stock are effective at building wealth FOR NOW.

It could have inherent failure modes you're not taking into account. For instance, if systemic crashes are built into the model, and 'anyone' as a class is substantially more likely to risk such crashes and lose everything, that changes the calculation.