system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why doesn't the government calculate my taxes for me? Or better yet, why don't they just take the correct amount out of my paycheck so there's no such thing as "doing taxes"?

So first off, all the tax forms I've been getting (from my employer, bank, loans, et cetera) say that the forms are ALSO sent to the IRS. 

So ... why doesn't the IRS just process all of these forms in some predefined system and have *it* do my taxes? Why make me do it where I'm prone to make errors?

OR, better yet, why not be even smarter about it and eliminate "doing taxes" by just taking the *exact* amount owed out of my paycheck rather than having me guess at a proper withholding amount and either owing money or getting money at the end of the year. 

It just seems like such a stupid and inefficient system this way - and besides, the government wants my money, they should do the work to figure out what I owe or put the proper rules in place so that the correct amount is taken out of my paycheck - why is the burden on me to do all this extra stuff?
gpt
That's precisely what the government does. They take the correct amount out of your paycheck.

Except it's not a perfect system. Your taxes depend on not just how much you earn in a year, but what you spend your money on that year. So the *precise* amount you owe can't be computed until after the year's over, and a full accounting of everything you made and spent is available.

Which is why you have to turn around at the end of the year and do the arithmetic and send in your forms. Because only then is the information necessary available.