There's NO paradox. The vast distances and the time it takes to travel them, even at lightspeed, is explanation enough. On top of that, civilizations need to exist in approximately the same time brackets since the Big Bang 14 billion years ago to be able to establish contact. Our civilization exists only a few thousand years… and it’s already doing its best to end it all before 2100 (Stephen Hawking warned about this century in particular being tricky).