Spoiler alert for one or several of the Alastair Reynolds' Revelation Space novels...
One reason you may not find anything....wolves.
In that series, there was an ancient war and the zealots left over were a machine race whose sole purpose was to keep such a war from happening again...by eradicating any races that rose up in tech. Yeah, that sounds weird but I did say they were zealots! They left honeypots, strange objects that could emit signals if disturbed by anyone capable of getting to them and breaking into them. That brought the "wolves" (as the humans called them in the story). It meant they didn't have to travel around looking for pesky awful life, they'd wait until it was capable of causing a nuisance and then they'd come around and wipe it out
Far-fetched? Sure, it's fiction! But who knows what motivation alien races might have. Hell, we've been to space and all we seem to be able to do really well is kill each other and develop tech that we use to numb our own brains.