They already know what your correct numbers are (that’s how they know when you make a mistake, learn the basics of double entry bookkeeping if this isn’t clear) and most other countries have much more straight forward income tax return systems.  influence behavior (feels like there should be a ‘u’ in there) through the tax code. Which the US Federal Govt finds a (politically) useful tool given the constitutional constraints on their power vs states over citizens behaviors through other means.