Perhaps, our entire country, including our security systems personnel became too complacent regarding threats on our soil. It was the "Won't happen here" mentality, even after the WTC bombing not that many years ago. How disappointing.
I wish you were right and it were that simple. I think there's ample evidence that the FBI sees every person whom they identify as linked to a terrorist organization as an opportunity to monitor and learn more. They manage to recruit a small number of these as informants, sometimes going as far as protecting the informants from deportation and/or prosecution, then go around chasing their tails trying to figure our how reliable the information is the informants give them.
The FBI needs a complete overhaul and a redefinition of its mission.