Many, and in fact maybe MOST, Americans aren't exactly fit enough to suddenly stop a crazed knife-wielding fiend who has plenty of past experience being violent, without getting badly hurt themselves. Very likely they'd get slashed or stabbed too. We don't know who else was there on that train or how capable they were. Whenever I pass by a bus stop most of the people waiting there are fat slobs, elderly or milquetoasty pacifist pipsqueaks with blue hair. In the case of the NYC subway attacker who was subdued and later died, there just happened to be a capable male present who took matters into his own hands. Jordan Neely also wasn't armed. If he had been things might have been considerably different. The girl in this case may simply not have been lucky enough to have a guy like Daniel Penny sitting nearby.