People Who Have Never Filed Taxes

I see all these posts of people who have never filed tax returns, some in their 20s and some even in their 40s.

When I look at my transcript on the IRS website, it includes all my income. So it would seem to be a simple algorithm to determine if a return is filed for a tax payer with income reported to the IRS. Kinda surprised in this day and age that people can go so long without filing a tax return.