Chris Wilson theorizes as to why we haven't gotten in contact with aliens yet:
It’s perfectly possible that our fantasy civilization would be 500 years ahead of us—but no more likely than its being 500 years behind us, or one billion years behind, or awaiting us one billion years in the future. The universe is about 13 billion years old, and Earth’s arrival on the scene 4.5 billion years ago did not occur at some divine moment of planet formation. It’s possible that this other, Earth-like planet was at one point dotted with thriving alien cities, that it sustained an intelligent species for millions of years, but that life there winked out at around the same time we humans were working out the kinks in having opposable thumbs. If so, our neighbor’s dying signals would have passed us by millennia before we could invent the radio dishes to capture them.
The Dish 