Tax frauds already know 'cash' income (sans withholrding) is often not reported so they're already an honor system anyway (Everyone is really -- even 'cash' is often reported on the 1099 too).
People using tax avoidance schemes through itemization or 'loopholes' wouldn't simply use a standard pre-filled form 1040 either, or rather, they wouldn't stop at that. Same goes for corp returns, dividend and interest income, etc.
With U.S. employers already transmitting wage and withholding data to the federal government, there's simply no good excuse not to 'autofill' it and/or just make the reconciliation & acknowledgement of those values easier other than an entire industry is vested in it being a complicated process most people would rather pay them (or use their products and services) to take care of.
People using tax avoidance schemes through itemization or 'loopholes' wouldn't simply use a standard pre-filled form 1040 either, or rather, they wouldn't stop at that. Same goes for corp returns, dividend and interest income, etc.
With U.S. employers already transmitting wage and withholding data to the federal government, there's simply no good excuse not to 'autofill' it and/or just make the reconciliation & acknowledgement of those values easier other than an entire industry is vested in it being a complicated process most people would rather pay them (or use their products and services) to take care of.