Banks file forms. Charities file forms. Employers file forms. They know how many kids you have, they know how old they are, they know if you own or rent, and how much your mortgage is and the interest being paid. They have info on your outstanding student loans. Except for the edgiest of edge cases, there really should be no surprises. Even a moderately powerful desktop should be able to precalculate the taxes for everyone in the country in less than a day.
Why is filing taxes even a thing anymore? Hell, at this point, I wouldn't be surprised if Facebook could do our taxes for us due to all of the info they have. Our tax system is stuck perpetually in 1960, and it's just sad to watch.