From a european perspective, having tax returns that are not pre-filled, and having a tax administration that doesn't strive to make payment as easy and quick as possible is nonsensical. Why would the state not want its services to replenish its coffers in the fastest most efficient way possible?
I wouldn't assume that the people who pay for tax preparation every year are idiots.
Please stop assuming the guy you're talking to on Hacker news is a simpleton.
The humans who make up the state are more keen to replenish their own personal coffers in the fastest, most efficient way possible -- good old fashioned graft. No one with significant power personally benefits from an efficient IRS with a pleasant user experience.