Fun fact: the US government has the ability to tell you how much you should be paying in taxes, and to pre-fill your tax returns. However this has been prevented by lobbyists from the tax preparation industry
"Fun fact: the {federal|state|local} government has the {information|resources|capability} to {something}. However, this has been prevented by lobbyists from the {group that opposes something or makes a killing doing something very inefficiently}."
Feel free to insert everything from tax filing data to broadband-as-an-infratructure.
This is only true if you have a relatively straightforward tax return. Once you itemize deductions, there are all sorts of things the federal government doesn't know about, like how much real estate tax you paid, how much you gave to charity, what your medical and miscellaneous expenses were, etc. They only know about what's on your W-2, 1099s, K-1s, etc.
For the really simple tax returns (like 1040-EZ), I think there's already an option to have the IRS compute your tax for you.