Okay, so, there are like four or five steps that must occur for a bystander to intervene in an emergency. When there are six people or more, the changes that all of those mental steps will occur is almost nothing. A man will stand in a room filling with smoke, filling out a form as long as the other people around him are being calm, someone can get stabbed on the street and no one helps, this man was trampled. The thing is, these all fit the patterns we know in human psychology. Bystander intervention in an emergency is incredibly rare.
Free advice: should you ever find yourself in a bad situation, put the people around you into a perceived risk or assign responsibility. Don’t scream, “Oh my god, call 911!” say “You with the blue and yellow shirt,” and once you have their attention, “call 911” or “help with this”. Thus it is that person’s job, they automatically shoulder some responsibility, they will stop. Similarly (though obviously in this situation a HORRIBLE idea) you are more likely to get help by shouting “fire!” which gets someone’s attention because it could put them at risk, than you are by just shouting “help!”.
Neither of those are fool proof, but statistically they have been chances of succeeding. Of course, anything is better than the more or less zero change you have for landing the one person willing to step outside and say “everyone here is wrong, this person needs help”.