The IRS has the income part of your return, not necessarily the expense part. Most people hit the standard deduction, but to do it right you need to actually do the expense part and compare.

Also they may have problems retrieving data in realtime. The IRS was a batch operation historically, and transitioning to realtime is challenging.

I mean what, are you going to do, put ip a wait cursor while joe bob mounts tape number 2,578,998,321?