Earlier quoted context omitted.
There's been dozens of hijackings since 9/11 https://en.wikipedia.org/wiki/List_of_aircraft_hijackings#20...
To be fair there's been a lot less hijackings in the 2000s and 2010s compared with previous decades - although as the decline started in the 90's - its not likely to be solely due to increased security.
- the end of the cold war, with the clear hegemony of the US which halted state-sponsored terrorism from unaligned-but-socialist-minded countries (especially Libya)
- targeted assassination of terrorist leaders and infrastructures (no more training summer camps) no matter the country they are in (mostly through drones nowadays), leading to a progressive reduction in sophistication in terror attacks committed, and the rise of lone wolfs instead of structured terrorist commandos.