There had already been books and movies with that theme, you can take it to the bank that hi-jacked airliners as an improvised WMD were on the radar at the relevant institutions.
The problem was that even if the information was available to them they didn't act on it timely.
I am saying they weren't prepared for the fact that such event could happen
And this is the same as expecting states to not apply surveillance despite encryptions
If we are not prepared, then it can happen
And if we don't want to be prepared by choice, then we let that kind of event happen