Pols have as Job #1 their own re-election and with a stirred up populace they are not so courageous as to buck a widespread trend of that sort. That's how Prohibition was repealed ... grassroots support for its repeal.
Well, the grassroots support for the FairTax is growing all the time and this can be observed by reading the comments to the President's Tax Panel. An awful lot of those commenting specifically identify the FairTax as the desired tax plan.
People doing a bit of reading of the bill itself and reading some of the informative material on the FairTax website is also helping.