(1) Quoting myself,

Such an entity would have special interest in Earth, not because of special interest in acquiring its resources, but because Earth has intelligent lifeforms which may eventually thwart its ends.

Receiving a signal from us would seem to make the direction that the signal is coming from a preferred direction of exploration/colonization. If space exploration/colonization is sufficiently intrinsically costly then an AGI may be forced to engage in triage with regard to which directions it explores.

(2) Creating an AGI is not sufficient to prevent being destroyed by an alien AGI. Depending on which AGI starts engaging in recursive self improvement first, an alien AGI may be far more powerful than a human-produced AGI.

(3) An AGI may be cautious about exploring so as to avoid encountering more powerful AGIs with differing goals and hence may avoid initiating an indiscriminate exploration/colonization wave in all directions, preferring to hear from other civilizations before exploring too much.

The point about subtle deception made in a comment by dclayh suggests that communication between extraterrestrials may degenerate into a Keynesian beauty contest of second guessing what the motivations of other extraterrestrials are, how much they know, whether they're faking helplessness or faking power, etc. This points in the direction of it being impossible for extraterrestrials to credibly communicate anything toward one another, which suggests that human attempts to communicate with extraterrestrials having zero expected value rather than negative expected value as I suggest in my main post.

Even so, there may be genuine opportunities for information transmission. At present I think the possibility that communicating with extraterrestrials has large negative expected value deserves further consideration, even if it seems that the probable effect of such consideration is to rule out the possibility.