It's impossible to automate the tax filing process unless you simplify the tax code.
And I've filed taxes in countries with simple tax codes where the government pre-fills out the forms. Guess what? You still need to go and double check everything because the information comes from your employer. I've found mistakes before. So I pretty much "do my taxes" myself to make sure what the govt sends isn't wrong.
This is a misunderstanding of the actual ask from the federal government and "automating" is a bit of a misnomer. The reason the IRS could theoretically fill out your taxes on your behalf is because someone else already submitted their part of the forms. Your employer reports your income, your broker reports your capital gains and assets, your bank reports interest, etc.. The ask is less about automation more not having to do those parts twice. The IRS could send you everything they've gotten about you and you just fill in the rest and/or dispute -- for normal single income wage earners there would be nothing else to add so it's effectively automated.
The gain is that we can make "doing your taxes" a non-issue for most Americans. Sure some people will still need accountants for complicated situations but in one swoop we can eliminate hundreds of millions of hours of useless work every year for basically no downside -- it's pure gravy.
And I've filed taxes in countries with simple tax codes where the government pre-fills out the forms. Guess what? You still need to go and double check everything because the information comes from your employer. I've found mistakes before. So I pretty much "do my taxes" myself to make sure what the govt sends isn't wrong.