Why do people ask "Why..." when it comes to human behaviour?

Sort of like my question. :)

People seem too often to ask, “Why do people do this” and “Why do people do that” in circumstances where there is no answer. Hideous crimes against children for example.

If we really knew what goes on in people’s brains, we would have discovered those answers centuries ago.
It seems like a huge waste of time.

The one thing we do know is that they did it. Everything else is subjective stumbling in the dark.