I'd imagine there'd be a "do you have unreported income or other unusual situations to disclose" step that'd open you to prosecution if you deliberately omitted stuff. It's not like they wouldn't do audits any more.
What OP is saying is that it's in the government's to keep things as they are, since if you overestimate your taxes by e.g. missing out on deductions, they won't have to make a correction on that.
[citation needed]. The IRS has asked repeatedly to introduce return-free filing, only to be blocked by Congress after their paymasters at Intuit and H&R Block voiced discontent with the possibility of their revenue stream being shut off.