The hijackers did not give the indication they were going on a suicide mission, just hijacking the plane. So people sat and did as they were told.
Secondly it's easy to freeze people up with a slight bit of intimidation; they're scared as fuck already (i think that's what Barry was getting at).
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"I'll never forget the moment during the lovely Alyssa Allure's scene in 'American Bukkake' where the fellow got out of his wheel chair to ejaculate on her face. It was grotesque but had a certain frisson." -Sock