[Cthulhu_]

Actually I'd argue that the scale / vastness of the universe is the main reason we HAVEN'T seen anything yet. I mean we can barely make out the planets in our own solar system, let alone asteroids - even assuming there's derelict spaceships out there several kilometers across, we can't really tell the difference between them and asteroids. Take Oumuamua, the asteroid (?) that passed through our solar system - even when all of our equipment was trained on it, we still could only make vague guesswork about its nature.

But anyway, that already assumes there's tons of spaceships out there, enough to actually show up on our equipment. Even if there's a galaxy-spanning civilization out there, the chances of running into them are low. I mean for a close analog, look at the game Elite: Dangerous, that can give you an appreciation of the scale of the universe - and in that game it's basically cheating because you can jump from one solar system to the next in seconds. And even at those speeds it takes forever to get anywhere.