Considering the fact that in billions of years of evolution only a few meteors have caused mass extinctions I have always been confident that we will not just happen to live in a time when one of the big ones hit. Human civilization has only existed for a very short time and I think it really would be like winning the lottery to get hit by a civilization ending meteor even in the next 10,000 years (although I'm no expert in the topic, simply looking at Earth's past).

Talking out of my ass here, but I'd assume the problem is one of resources. While unemployment may be high, demand for "smart" people (which you'd need to work on anti-human threats) is way to high. Combine that with technological feasibility, and the resources could probably have been spent elsewhere better. Today though, the technology is probably "common" (relatively speaking) enough to spend some resources on the problem.