Earlier quoted context omitted.
This is not done because the IRS doesn't have the power to enforce its tax system, and if it reported the information it had to the people, the people could know they can slip away with not paying anything that wasnt properly reported. First, a transparent system of the IRS would lower revenue. Second, the deductibles system is very complex for the IRS to pre-calculate it, so they are unable to do it.
You didn't cover the most important—and political—reason: it would delay refunds . 2019 deadlines for 1099-INT/DIV (i.e., the forms you get from your bank or brokerage) are April 1st. The IRS filing window opened January 29, with 90% of tax returns processed within 21 days. Since the IRS can't reliably pre-populate a tax return without all the required information, it would delay filing (and refunds) by 8 weeks. As t…
This doesn't really pass the smell test for me. The IRS has, what, 7 years(?) to audit your tax return. They can and will do so, and will send you a bill, with penalties and interest included. (Source: this has happened to me, around a mistake I made with self-employment tax the first year I had non-W2 income.)
Not sure how you'd be "long gone", either, unless you're not a US citizen and have since moved out of the US.