The biggest force in lobbying against these kinds of tax reforms is surely Grover Norquist and his Americans for Tax Reform. Grover has an iron grip on the tax policy of the Republican party. Virtually all republicans sign his pledge to oppose any and all tax increases. And they are opposed to anything that makes filling taxes easier:

Tax preparers have a vested financial interest in taxes being difficult, with Intuit even going so far as to say in a filing with the U.S. Securities and Exchange Commission that federal and local governments making taxes easier to file was a "a continued competitive threat to our business." ATR's interests align with this in that they desire to keep taxes difficult to stoke anti-tax sentiment. That is to say, if paying taxes is "too easy", then people will be less likely to fight taxes in the way ATR wants.

Norquist and the ATR have publicly argued that things that make tax filing easier on taxpayers constitute an automatic income tax audit on every taxpayer, and serves to keep people uninformed about how taxes work, and was an attempt by the IRS to "socialize all tax preparation in America." In a 2005 presentation to the President's Advisory Panel on Federal Tax Reform, Norquist representing the ATR argued that if taxpayers did not have to prepare their own taxes, it "would allow the government to raise revenues invisibly."