History is filled with people who dug their own graves while a person with a gun pointed at them told them to do it.
It takes an exceptional person to act before their fate is sealed and the majority of passengers, if not all of them, will be in a state of denial or shock at the situation they are in preventing them from action. Others who might want to act, but not having been in the situation before, will think about what to do or when the right moment to act is, and the right moment will never come, especially if the hijackers can guarantee the first person who acts dies.
It takes an exceptional person to act before their fate is sealed and the majority of passengers, if not all of them, will be in a state of denial or shock at the situation they are in preventing them from action. Others who might want to act, but not having been in the situation before, will think about what to do or when the right moment to act is, and the right moment will never come, especially if the hijackers can guarantee the first person who acts dies.