Maybe our civilization is the only one living in an Oprah world where reaching out to other civilizations is thought to be beneficial. Civilizations tend to war with each other on Earth.
Another point is that maybe they just don't want us to know that they are there for their own reasons. Perhaps we are too primitive to be taken seriously.
Another point is that space travel might not be restricted to speeds that our limited science understands in 2001 AD.
Don't any of y'all know that Agent Mulder proved beyond any doubt that "they" are out there. Now what are we to believe since his contract was not renewed? (and I, for one, miss him--the new guy is NG but the chick is still lookin'good!)