They didn't. The difference between today and a hundred years ago isn't actually in what people did. It's how many people did a certain thing. Back in the day people didn't invest because they were farmers. Nowadays a lot more people live in cities and have a high enough income to invest it and this requires financial services to scale to millions of customers.
With dumb commission fees and other policies that made it deliberately obtuse and painful for the retail investor. Even today, with any brokerage, you can't freely trade without penalty unless you pass the class based virtue signal of having $25k amassed in your investment account.
Everything was still frictionless when the world was you dictating your thoughts into a nearby phone/ear while someone else made all the magic happen. In pure friction terms, robin hood with their lag and issues filling orders is probably still a big step down vs. calling your broker in a panic and dictating trades.