First of all, I do agree with you that why haven’t other civilizations created AGIs that have then spread far enough to reach Earth is a really interesting question as well, and I would be happy to see a discussion on that question.
For that question, I think you are missing a fourth possibility, AGI is almost always deadly, so on quantum branches where it develops anywhere in the light cone, no one observes it (at least not for long). So we don’t see other civilization’s AGI because we just are not alive on those quantum branches.
Thank you for this, I still read it periodically.