For all you know, He never chooses to intervene. We make good choices and bad choices and all He can do is sit and watch. Natural disasters happen, they kill thousands of people, He doesn't intervene on that. It isn't his place. I think you're supposed to trust Him and have faith in Him that what happens in this life, no matter how bad, isn't the end of it. You've got to make the right decisions in this life to have passage to the next one, which is when He'll do the intervening.
As for the situation you're talking about, those are human choices. Or semi-human, if you want to look at it that way. Not everyone is a good person. I guess what they mean is, if God intervened on everyone's behalf, there'd be no good or bad in the world. And if there was no bad, then wouldn't Satan be getting awfully bored? And whose to say he doesn't do his share of intervening?