The thing people misunderstand with the government not being able to figure it out is because there's a huge variety of complexity that is truly individual based. Did you make a contribution to a tax deductible IRA? Did you make a retroactive payment to that account in the following tax calendar year? There's a ton of variables going on here, where the government doesn't have this all-seeing system where everything gets accounted for across the vast array of income sources and employment statuses, dependents, filing status, and all the increments and decrements to those things through time. There's no one central source where all this information is collated and waiting for someone to turn the crank and grind out a number from. Folks have to remember that nothing is implemented by default.
The effort to reduce the complexity of the 1040 into 6 new schedules was a great way to factor out those with complicated situations such that the majority of tax payers are oblivious to those nuances. The crux of the matter is that legislators passed into law all these onerous mass of rules to turn various levers to entice and discourage certain things and bite those with progressive tax rates. It is precisely the existence of these rules as to why the government doesn't know what tax valley you land in that huge parameter space. It will not presume to know your specific circumstances but assume that you being aware of your own money and circumstances are in the best position to know these things. At the least one thing I learned is that with tax laws if you have no idea what a thing is it probably in not applicable to you.
Needless to say all of this would be much more simple if we just pay a flat tax on all income for all people. Nothing simpler than that.