There's also been none since I washed my hair this morning - certainly must be related!!

I don‘t think that is true at all. There have been numerous hijacked planes since 9/11 including two in the USA just this decade.

https://en.wikipedia.org/wiki/List_of_aircraft_hijackings

Plane hijacking has been on its way out anyway after the turmoil of the 1970s. And that has probably more to do with a) the relative political stability of the post cold war period, and b) a general sense that airplane hijacking isn’t actually that likely to advance your political goals. If you read the list above, you see people hijacking planes all kinds of dumb methods, hardly any of them involves carrying an actual bomb onto the plane.