Heck! Even the president's tax reform commission refused to evaluate the FairTax bill as it exists but instead came up with a construct of their own to shoot down.
And those aligned against the FairTax such as certain persons in Treasury refuse to show their data or discuss their analysis methods. They know their analysis methods are flawed.
They claim the micro-datasets used for analysis must be protected for taxpayer privacy yet they could easily scrub identifying information and release their data as is normally done in the process of secondary analysis. Off the record their analysts have admitted they are hiding and avoiding challenges because of politics.
That situation will not last too much longer as the delays are not going to be tolerated by Congress.