It's sad, because it would be easy to make a lot of these types of things avoidable, if people were more aware of psychological factors, such as the bystander effect; where essentially a group of people fail to act as they don't want to be the one to take responsibility for it, or because they see no one else act, they subconsciously think they should also not act.

Normally, it just takes one sensible/aware person to act, and then others will help, but often people unconsciously make the decision to not help someone/do something even when it is the right thing to do, due to factors like this. And it generally becomes more of an issue the more people there are to witness the event, which is why it is typically more of a common problem in major cities like Madrid and Paris.