[gfodor]

If you assume a civilization (or AI singularity) eventually stops worrying about destroying itself, and the bulk of the risk to it stems from external civilizations unleashing galaxy destroying technologies (perhaps unintentionally), it seems logical that if a) such probes are technologically feasible and b) life can originate in places beyond Earth with some meaningful probability that you should expect to find a galaxy-wide network of autonomous probes specifically engineered to cut down the blast radius of these kinds of existentially risky technologies. Odds are, if that's what these are, they are old, autonomous, and should present evidence they are here to primarily prevent our mistakes from leaking across the galaxy, and secondarily perhaps to help preserve our civilization in those scenarios insofar as it is not in conflict with the primary objective.

[meowster]

Perhaps are afraid that making themselves known would increase the chances of others developing galaxy-destroying technologies.