But if what you say is true and the IRS can't calculate what you owe, that would mean they have absolutely no idea what you should be paying and you could get away with paying basically anything you want as long as you're not randomly selected for audit.
I live in Scandinavia and that's how it works here: you basically get a proposal based on what the tax office knows (salaries, local capital gains/losses, interest deductions if you have mortgage etc.), and then you submit diffs, if any, and they calculate everything based on that.
I've only ever had to change my tax proposal when I've married/divorced/had kids or had activity in a brokerage firm abroad (who wouldn't report my gains directly to my local authorities). Buying and selling property also shows up automatically as the registration process goes through the government anyway.
Now the tax authorities have even stopped sending any papers with a return envelope. They just point to the online service where you can easily augment whatever fields that might be missing input.
The IRS has some information about what you make obviously, because employers withhold your income. But they have very little information about deductions. Of course the IRS could calculate a maximum tax amount and put the burden on you to apply for deductions, but Republicans would flip their shit because it’d be a huge effective tax increase. They want tax season to be painful every year.
Which gets to the point that is whizzing by everyone’s head. Intuit and Quickin aren’t single handedly lobbying to keep tax filing complicated. You could probably crowd fund an opposition if that was true. Intuit and Quicken are leveraging a political situation that exists for other reasons.