>They already do your taxes in the background to confirm your return is correct This is a common misconception. Most places that send you forms also send them

>They already do your taxes in the background to confirm your return is correct This is a common misconception. Most places that send you forms also send them to the IRS (but by no means all places). The IRS makes sure that the information you put in your forms is the same as the forms they got, but they know nothing about your dependents, whether you pay mortgages interest, etc. Now, the counterpoint to that argument is that c.90% of people just take the standard deduction anyway now that there's not SALT, but the argument there is that we should move completely away from deduction-driven taxes (which is probably the solution). As for TurboTax et al, those places are not sending your forms to every state tax agency (why do people always forget about state taxes in these threads?), so there's still very much a need for some solution there. Probably IRS data sharing, but good luck getting all the states to agree with the Feds on tax forms (just look at the SALT battle).