Back when it was just nation-states keeping tabs on each other; before cell phones were cheap and ubiquitous and terrorist organizations could easily get their messages out and travel to "enemy" lands or find converts there to blend in with the native population until attack day arrives.
Threats can come from individuals now, not just nation-states. Weapons available to individuals can do a lot of damage. I don't envy anybody charged with preventing serious attacks that could come at any time from almost anyplace.
Much of today's massive spying infrastructure has largely been built up since 9/11 at a time when privacy concerns were not at the top of the agenda. The safeguards probably need a comprehensive review and reconfiguration now that there are significant protections in place and the ongoing issues are better understood. The panic has passed.
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