[jswhitten]

Because the timescale of the universe is much longer than the timescale of human civilization or intelligence. The odds of any aliens we meet being at the exact same level of development as humans (to within ten thousand years or so) despite having evolved independently on a planet billions of years old, are extremely small. In the vast majority of cases they will be millions of years more advanced or millions of years less. As chimps don't build starships, it follows that almost every interstellar civilization we find will be godlike compared to us.

In other words, we are a newborn intelligent species, and newborns generally find that everyone around them is older.

[mtdewcmu]

You're assuming that being older implies having more capabilities. Civilizations like ours almost certainly reach limits, either in terms of resource limits, or in terms of fundamental limits on the kinds of things that can be engineered (or both). The fact we've never run into any alien tourists or explorers, despite thousands of years of record keeping and being able to search the earth for alien artifacts, and our own research into star travel support the idea that it's impossible.