IMO at least as plausible an answer is that species with the capabilities to produce such probes also have good reason not to do so. We ourselves arguably have

IMO at least as plausible an answer is that species with the capabilities to produce such probes also have good reason not to do so. We ourselves arguably have good reason not to broadcast our presence, reasons which we have come to belatedly but which are now widely known; e.g. the widely-cited belief that 'whenever' two cultures of significantly different technological prowess have interacted, the less-advanced one invariably went extinct / degraded / whatever. I haven't read it yet but IIRC the Three-Body Problem trilogy proposes a universe in which advanced species stay silent for fear for just such interaction. I can myself propose a variant idea, which is this: if we conclude from perceived silence/solitude that other species are likely out there but keeping their heads down, ...maybe we should do the same, not knowing what we might invite by broadcasting our presence. If the first species to encounter this question incorrectly guessed its own probability of being first, and came to the same conclusion, we might actually be surrounded by a saturated sea of advanced species... all playing it unnecessarily safe... <shrug>