One of the hurdles here is that the IRS has increasingly deputized tax preparers as their first line of enforcement via preparer penalties [1].
Another is that a free filing system with pre-populated returns shifts the information asymmetry involved in tax filing to be fully in the taxpayer's favor. Many people have an "I need to report everything because I don't know what the IRS knows" mindset. If the IRS populates a taxpayer's return with all the info they have, there's no incentive to report anything not listed.