There's a depressing non-wolf Great Filter argument. What if this sort of scenario is unavoidable for fundamental reasons... possibly involving a combination of thermodynamics, evolutionary dynamics, and game theory.
For this to be an explanation it would have to be that this "great filter" is so hard to avoid that someone escapes it maybe once per few thousand galaxies per many billions of years.
http://en.wikipedia.org/wiki/Olduvai_theory
For this to be an explanation it would have to be that this "great filter" is so hard to avoid that someone escapes it maybe once per few thousand galaxies per many billions of years.