Edit: Also, as the tax base gets smaller, I can see some of the tax advantaged accounts people have money in become not so tax advantaged. The money to replay all this debt (including infrastructure, environmental, and policy debt) has to come from somewhere, and I'd bet it's both from inflation and savings. Or someone hits the reset button with a revolution or war.
That's not because there is a high bar to investing, it's that most people are financially undisciplined. I see it all the time, people get a bonus and the very first thing they do is go buy a new car. Literally one of the worst things you can spend money on is a car, and a new one makes it even worse. Many people carry CC debt, which is absolutely crazy. Keep in mind I'm not talking about people who are struggling just to put food on the table, but people who should be able to save, but instead do really stupid things with their money.
2. If you only have $25 left at the end of the month, you shouldn't be investing in stocks at all. You should be putting your $25 in a savings account for emergency expenses.