It's good to have reminders of these effects, because they are large and important for anyone hoping to impact behavior, altruistically or otherwise.

Rather than see it as a mystery of "why don't we help each other more?" I think it's better to think of this as "how do we get people to help each other more, and more usefully?" or in two parts: "How do we get people to do things?" and "What things should we get people to do?" None of this seems intrinsically linked to altruism as such.