Edit: Not sure why I have negative points here, I was just saying that the process of implementing a system to actually get people their taxes and accommodating all the edge cases and ensuring everything is perfect enough that people literally don't have to do anything is probably not worth it compared to doing a check of submissions against the IRS own findings. Feel free to tell me why I'm wrong, I'm all ears and not super knowledgeable on the system (obviously)
EDIT2: Also, not implying that it can't be done, just that it's not worth it to the IRS to do something like that. Seems like otherwise it already would have been done?