author says their projects "underscore the critical need to quickly establish regulatory frameworks...
Ah, a sneaky argument for more regulatory capture in favor of established players. Or another wannebe little dictator. Or both.
The thing is: Whether AI or biological intelligence, the signs of a civilization are likely to be much the same: engineering structures, electronic signals, alternations of natural events (atmospheric composition, maybe even orbital changes).
The most likely explanation is simply distance. We cannot see anything as small as a planet at interstellar distances. The best we can do is notice the miniscule dimming of a star, if the orbital plane of the planets allow them to pass in front of the star from our perspective. If we cannot see planets, we cannot possibly see any but the most massive engineering structures - on the scale of Dyson spheres.
Signals over interstellar distances? While Earth went through a fairly noisy electromagnetic period, the signals were still to weak to be picked up (by our level of technology) at the nearest star. As technology advances, we no longer need hundreds of kilowatts for ordinary radio stations; indeed, most signal traffic is now using fiber optics, which are not detectable at all.