US Tax law is far too nuanced and complex for this. Just simple things like donations create issues.
Donations to registered 501(c)(3) charities are tax exempt. But how does the IRS know if you gave the Salvation Army bell ringer $20? You have to tell them. On your tax return.
Medical expenses in excess of 7.5% of your income are also exempt. And the IRS has no clue which of your expenses were medical. So you have to tell them.
It's far more involved and complex than even just this. Did you move? Are you a member of the military? Costs related to your move are not taxable.
There are probably thousands of potential exemptions. Few of which could be automatically identified and credited without massive privacy issues. And even then couldn't be perfect.
That cardboard box you bought at the local big-box store? Was it a tax exempt moving expense?
Oh, and the IRS has been sitting on my return for 2 months now and I did all the work for them. Could only imagine what it would look like if they had to track all of this.