It's important to remember the distances involved here, wherein the question of 'why haven't we seen them yet?' is probably just that it takes too long to see things. Its over 4 light years to the nearest solar system, over 25,000 to the next galaxy, so to see something in a telescope from that far away the information is already at least that many years old for the light to have traveled back to our eyeballs. The whole of recorded human history is only like 5,000 years old, there could be a civilization the next galaxy over that's 20,000 years older than us by the time we see the evidence that they're at our level, they could have been colonizing our celestial neighbor proxima centauri for the last 3 years and we wouldn't know yet, and if they could only observe neighboring systems by observing light same as us they wouldn't know we're here yet either. The light that makes up the images that will be an alien's first glimpse of our existence is already traveling to their methods of observation, but it could still be millions of years before we're seen. It's too abstract to bother dwelling on, we still need to figure out how to kill all the goblin sharks or what are we even doing, as a species?