Consider the energy and material engineering necessary to achieve long-distance space transport of any sizable amount of people, equipment, and supplies. Regardless of whether the transport is subluminal or FTL, the energy requirements are tremendous and the engineering requirements for a durable vessel astounding.
My guess is that by the time our materials science and our energy production are up to the task, our interests may well have changed - because (and here I speculate wildly) science at engineering at that level will reveal so much about the fundamental nature of the universe and give us so much interesting practical technology that biochemical life clinging desperately to lucky rocks in the lucky zone won't be near so interesting anymore.
No one comes near because we have nothing to offer those able to come near and get home again to report what they found.
As to simply detecting signals, we have to consider how lucky we are to have so much ore so close to the surface: Metallurgy and eventually radiated communications were a natural for us.
Other civilizations may well start with fantastically engineered wood and eventually plastics, and go all-fibre, all line-of-sight, and have very, very different communications systems, systems undetectable at any remove.