That the IRS does not have all of the necessary information until after individual tax returns are due is probably because people have to file their own taxes.

That the IRS does not have all of the necessary information until after individual tax returns are due is probably because people have to file their own taxes. They don't need those forms until people file their own taxes, because they don't need to verify until after the taxes are filed. That can be changed, if we want the IRS to send people provisional reports that say, "Here is what we think [you owe | we owe you]. If you agree, sign and return. Otherwise, file using the appropriate forms."