A suicide bomber doesn't need to worry about airport security at all. They just need to figure out when the airport is at its most crowded and stand in a check in line and detonate their bomb.
A wearable bomb can only kill (say) few dozen people, even in a crowded area, but the same bomb detonated on a 747 could kill 400.
It could also allow them to gain control of the aircraft (maybe, depending on whether they can persuade the people on board that they aren't planning to crash it into anything).
Suicide bombers generally aren't rational folks who multiply "number of infidels I can kill" versus "chance of being caught" though. And we should be thankful that they aren't so rational.
I don't know why they're not already doing this. In fact, they might be better off still just walking in with machine guns and shooting as many people as they can. You could probably mow down a lot at a crowded airport.
It makes me think that we're doing a pretty good job of keeping most of them out of the country in the first place. Otherwise I think we'd be seeing a rash of smaller scaled, highly targeted incidences like this.
