[sokoloff]

The largest blocker in my experience is that they don't have that information processed for 6-18 months after the filing deadline.

Source: personal experience with a period of very-late filing in my younger and dumber days.

Other factors are that they can't possibly know your total liability. They literally don't know exactly what you owe them.

Cash-based employment or trade, sales of securities purchased prior to the very recent cost-basis rules, basically anything schedule C or E (small business or rental property), etc, etc.

They might be able to auto-file something close for the simple W-2 employee case with no investments, but they don't have a secret computer system with your full return auto-prepared and just waiting to catch you for forgetting to enter $12 in bank interest from a long-forgotten account.