What would it cost the US government to buy out the major tax prep providers? The IRS could then provide free tax estimates to a large percentage of filers, and hire many former tax prep workers as IRS agents.
People just don’t care enough (a state like California could make it illegal to charge for e-filing, for example, but they don’t).
To save even more money, I wonder if they could even take a page from real estate law where easements for public benefit are sometimes purchased either through the free market or via eminent domain. Under this theory, they wouldn't even have to purchase full ownership of whatever's necessary for US filing purposes, they'd just need to purchase an easement transferring to the federal government Intuit's right to charge US citizens and resident noncitizens for US federal income tax filings via TurboTax, as well as the right to deny these groups TurboTax's US federal income tax filing services. And then the federal government would decline to exercise these two transferred rights.
But yeah, I have no idea if the easement idea would hold up in court, and in any case I doubt the government would be politically willing to use eminent domain against Intuit despite indisputably having the right to do it.