When I'm to do my taxes, I get an auto generated draft and the only thing I have to do is click the "Accept" button.
You only have to fill your taxes manually if you're self employed or have some sort of earnings other than your job, in which case, the company that does you accounting, does the taxes for you too in 15 min.
But it's against the law. The law specifically prohibits the tax agency (IRS) from providing pre-filled tax forms for taxpayers. Why? Who knows... I can't read the minds of Senate and House members! But I'd very confidently place a bet that it's entirely because of careful lobbying by the two companies (Intuit and H&R Block) who make large amounts of money off the current system.
References:
https://www.vox.com/policy-and-politics/22596072/irs-turbota...
https://www.propublica.org/article/turbotax-just-tricked-you...
They know the money you make, they can make it free and easy but they don't want to cut the middleman.
You have entrenched interests keeping the whole process as difficult as possible.
A person up the comment chain in Spain said that's not the case there, and i can confirm the same for France - everything they know is pre-filled, and it's up to you to declare the rest. Of course some people will underreport, but so will those willing to in the American system ( for tips, cash payments, freelancing they can be fairly certain the IRS can't know). Nothing changes besides middlemen lining their pockets and regular people losing time.
The problem the IRS is trying to solve is collecting taxes on money they don't know about. For example, if you sell illegal drugs, you should be paying tax on that income. But obviously you don't report to the government the amount of illegal drugs you sell. So they can't just send you a bill for your taxes.
It is odd that every American has to suffer for this obscure corner case, but they probably lose a lot of revenue if they stop taxing drug dealers, so here we are.
It's not the IRS caring about losing revenue, but lobbying from tax firms that's the problem.
The main problem tax returns are trying to solve is that Americans aren’t enraged enough at their taxes to demand lower taxes (on the rich) or a much simpler (and regressive) flat tax. I posit that there is no technical or financial incentive at all, and that the aim of the tax filing regulations is entirely political.
But if I understand correctly, that corner case isn't even "real". Suppose you were a drug dealer in a country that automatically handles tax, and most citizens don't need to file a return, e.g. the UK. I'm pretty confident you can still be prosecuted for failure to report the income from your drug dealing, just as you could be for not reporting any other income where the tax wasn't removed from the paycheck.