Because big $$$ is more important than actual security.
Because Haliburton and the Bush family would lose oil contracts?
We know pretty well that Osama was paid off by the Saudis to not go after them. We know that high level members of the Saudi elite are funding Osama. We know that 15 of the 19 were Saudis. We know that the Saudi Ambassador to the US's wife was helping fund them.
We also know that until we stabilize Iraq, and stop attacks on the pipelines, the Saudis have us by the cojones. The Bush clan and the Cheney/Halliburton crowd do realize this, and are acting "prudently", but it hasn't upset their morals enough to stop profiting off deals with these murdering Wahabi bastards.
Oops. There are (R)'s behind their names. I apologize. Nothing to see here, move along.