Because in America, as in almost all other countries, power resides with the very wealthy. It is absolutely not in the interest of those with huge incomes - corporate and individuals to have a tax system that has no loopholes.

I have recently heard that 68 percent of the top 100 companies in America paid zero taxes in 2003. From their perspective that is a ton better than a flat tax that is unavoidable.

Our politicians, both republican and democrat, are "purchased" by campaign contributions. If someone like tobacco farmers pay enough they can get huge farm subsidies and billion dollar buyouts. (That buyout was approved today - your tax dollars at work!))

Likewise, large corporate and PAC contributors can, and do, get massive loopholes. That would stop if we had a flat tax that was unavoidable.

Lastly the idea of a flat tax sounds great, but implementation would be difficult. Would we want to exempt anyone? How about churches, 100% disabled vets, very low income working families, etc. etc. Once you start making exceptions the special interests will fire up again and find ways to get their exemptions too.