Here's the thing: if you have just killed five people, "give me $100 or I will kill you tomorrow" becomes a much more effective threat.
One-time games and repeated games have different strategies.
It becomes more effective only because it changes the probability estimation of the outcome.
Life is a repeated game of decisions that compound on each other, so that difference is irrelevant.
There's actually a similar though experiment that might seem even more bizarre: I could tell you "give me $100 or I will kill you tomorrow" and you probably wouldn't give me the $100. That's because when it comes down to it, humans don't see the loss of their life as that big a deal as one might think. It's a big deal, of course, but in combination with the low likelihood, still not big enough to forgo the $100.