In this context, it actually makes sense to think in a human-centered way.

Consider how many planets are capable of supporting intelligent (as we know it).

Now suppose we detect evidence of industrial behavior (certain pollutants, nuclear detonation, etc).

Would we not laser focus on that one planet and observe it with everything we have - including sending reconnaissance drones?

Furthermore, would we not want to avoid detection where possible, in case life does exist on said planet and it turns out to be an existential threat to humanity?

Also, it would be trivial to avoid detection in our own solar system. Duck behind a moon or planet, or just quietly float in the blackness of space, and no earthling will ever see you.