Earlier quoted context omitted.
Democrats have the entire government now, President, senate and the house. Democrats had filibuster proof majority when Obama was president. Why are you just blaming Republicans?
Because of Grover Norquist and his organization (ironically named Americans for Tax Reform). Their "Taxpayer Protection Pledge" taken by most Republican lawmakers (95% before 2012), locks them into supporting his policies. The problem is that he views any attempt to simplify tax filing just like a tax increase (presumably since people will be less upset about paying their taxes), and uses his influence to lobby again…
If the taxpayer agrees, they can just sign and get refund or pay additional taxes.
If taxpayer disagrees, they can submit additional information.
The Democratic president can do this right now, for this tax year.