The CIA was a stunted place in 2001.
The Aldridge Aims scandal had left deep scars in all of the directorates. Worse, the FBI had been charged with the mole hunt instead of their own internal affairs, and this lead to the open hostility between the two agencies which became the important backdrop to the intelligence failures of 911.
Whereas the FBI, of course, was dealing with such fun stuff like Ruby Ridge, Waco — and Robert Hanssen, who was eventually caught. In early 2001.
The entire US national security structure (and hell, much of the federal government as a whole ) had been set up to explicitly counter the USSR. After 1991, practically every department and agency’s very mission was in limbo.
Meanwhile, everybody in the post-Cold War era was screwing up and having major PR crises, from the scandal-prone Clinton administration to the US military itself in humanitarian/peacekeeping operations gone awry. This was the era after the End of History, where globalization and free trade capitalism would solve all problems and Democrats and Republicans could compromise on ending the Era of Big Government and Peace Dividends even as politics became an increasingly partisan bloodsport between Gingrich Republicans and Clinton Democrats.
The general public — and many in government — were more worried about drug dealers, school shooters (Columbine), and illegal immigrants from Mexico than they were about suicide bombing Islamist terrorists, which most people assumed was a problem for Israel, not America. (Obviously, we’re still worried about illegal immigrants — look at who the President is now — and the rest of the aforementioned, but since 9/11 we’ve added Radical Islamic Terrorism to the list of things to be scared about).
To the extent terrorism was a problem, or seen as a problem within the US, it was the Unabomber and Oklahoma City and Eric Rudolph. A lot of people assumed that the 1993 WTC bombing was a one-off, rather than the beginning of sustained operations that led to 9/11. And besides, the FBI got all or most of the guys who did that, right?
Bottom line: Americans were more worried about Y2K and more interested in the lurid details of Bill Clinton’s sex life than they were about the threat posed by al-Qaeda. And the US government declared victory after the fall of the USSR, and deliberately cut budgets across the board. The free market won, Communism lost, and the New World Order was upon us, and liberal democracy would eventually spread everywhere organically and naturally, because why wouldn’t everyone in the world want to emulate the US? That was the general attitude from 1991-9/11/2001.