And why? Probably because they actually believe their own Tiny Minority of Extremists line. From [1] Insight Magazine:

The U.S. intelligence community has been shaken in its failure to predict Hamas's victory in Palestinian legislative elections.

The intelligence failure came despite a Saudi assessment relayed to the United States that Hamas would win the elections. Officials said the CIA was influenced by an Israeli assessment that predicted a victory by the ruling Fatah movement led by Palestinian Authority Chairman Mahmoud Abbas.

"There are a lot of questions going to be asked when the dust settles," an official said. "The biggest question is: do we really know what's going on out there?"

Nope. I think they should read Jihad Watch.