As a supporter of the Fair Tax, I completely agree, however I think there are two reasons why it won't happen:
1) Entrenched interested in the current system (Accountants, the IRS, politicians, etc) who wouldn't want to see income tax and the complicated system go away
2) The fear that people will really see how much of their money goes to taxes.
#1 prevents a national tax because people don't want to have a new tax, they want a replacement tax. It will be very hard to eliminate income tax in my opinion.
#2 is a real concern because under the current system, no one knows how much of the cost of an item goes towards taxes. If you asked me what percentage of my income went towards taxes, I couldn't tell you. Between matching taxes my employer pays, deductions that I take, taxes that are built in to the price of all the goods I by, etc, there's no way to know. A lot of people will be pissed when they see a 23% VAT (30% sales tax) on everything they buy because for the first time, people will really know that a quarter of all their money goes to taxes.
For those not familiar with the topic, the Wikipedia article is an exceptionally good read in this area: http://en.wikipedia.org/wiki/Fair_tax