According to the article:
After the Sept. 11 attacks, the Bush administration and senior American intelligence officials quickly decided that existing laws and regulations restricting the government’s ability to monitor American communications were too rigid to permit quick and flexible access to international calls and e-mail traffic involving terrorism suspects. Bush administration officials also believed that the intelligence community, including the Central Intelligence Agency and the N.S.A., had been too risk-averse before the attacks and had missed opportunities to prevent them.