> Most people tend to assume somebody else will take initiative. Also, you can show incontrovertible evidence to a crowd and they may still express apathy (e.g. the Kitty Genovese case).
For the curious, I recommend reading some recent reexaminations of the Kitty Genovese case. Most people's perception of it is as a demonstration of the bystander effect, but if you look more closely, that is not a very honest take of what happened. That angle however is something that shocks people and grabs attention, which makes it a very successful meme.
Rutget Bregman writes about this in his book Humankind, as well as other similar cases. Some snippets of it can be found online.