Earlier quoted context omitted.
That's just income. There is also the issue of deductions and credits, which covers many more people. The income portion of my taxes takes me about 5 minutes. Most of my time is spent on the deductions and credits portion.
Seventy percent of households take the standard deduction or have no income: https://taxfoundation.org/who-itemizes-deductions/
Most people are just afraid of making mistakes (it's not a big deal if you do, you'll get a notice and you file an amended return). Or maybe they just feel their time is too valuable to spend an afternoon filling out forms. But most individual tax returns are really not that complicated.