Far fewer people were subject to the income tax at the time. The average Joe who couldn't read well or do much arithmetic didn't have to worry about it. For

Far fewer people were subject to the income tax at the time. The average Joe who couldn't read well or do much arithmetic didn't have to worry about it. For this reason the Social Security tax was implemented as a payroll tax. The tax was intended primarily as a tax on the wealthy or middle class, but over time by not adjusting the standard deduction/exemptions, more and more people ended up paying the tax. You could also make the argument that more and more people became middle class.