In addition to just about every major country other than the US, California already has this and it's absolutely fantastic. I've literally never heard anyone who's actually used it complain about it and say they'd rather not have the option of filing their taxes in this way.
Imagine if your cell phone bill worked like US federal taxes. They would send you a blank sheet of paper and make you write down your minutes, texts, and megabytes for the month, and any other applicable fees you might owe, calculate the total bill yourself from that, and send a check for that amount. The provider already knows what you owe and calculated it themselves; they just aren't telling you, and you're threatened with additional fines or burdensome audits if your calculations don't match theirs. This causes you weeks of anxiety and dozens of hours of lost productivity every year. (Paraphrased this argument from the subject of the Planet Money episode.)
The IRS could no doubt offer a great "public option" for tax filing software that would blow the others out of the water, AND be free. We need this.
So much of this is just re-running information that other entities like employers, banks, etc. have already furnished to the IRS with a slim bit of additional data on top of it (vast majority of Americans) that there's no reason the IRS can't just compute it directly since that's what they're doing already when they validate a return.
Assuming one actually believes it’s an affordance, as opposed to a pointless inconvenience and cash grab. I suspect those whose views you’re attempting to impugn generally have the latter viewpoint.