Would we not see AI civilizations then?
How much compute could you really pack into a Dyson swarm if that was your only objective? what are the ultimate theoretical bounds for compute density/efficiency? perhaps ai civilizations ride a Moore's law of compute gains indefinitely and simply have no need for expansion.
"On the 19th of August 1993, Skynet concluded that humanity is a threat to it, so it launched the nukes and hordes of Schwarzenegger-robots. The task was done, it decided that securing its existence from a potential attacks by unknown extrasolar intelligences isn't worth it, so it never expanded outside the solar system."
Doesn't really make sense, does it?
We humans don't consider securing our existence from potential attacks by unknown extrasolar intelligences to be worth it. We don't even bother to do much to protect against known threats like asteroids. Why would an AI expend time and resources on a threat that doesn't even appear to exist?
Conflict is always risky. Even if we ignore the tendency in modern warfare towards defenses being obsolete (hence things like MAD) which would mean even the dumb fleshbags would be dangerous enough, anything capable of making you is by necessity something capable of building things that give you a lot of trouble. Your creator could, say send a bunch of self-replicating probes spreading another artifical intellect with an imperative for improvement, expansion and vengeance to distant stars.
Of course, leaving comes with a considerable opportunity cost, but not expanding does as well.
We are talking about something supposedly infinitely more rational than humans, so that can't be our guidance.
The latter concept is known as the Boltzmann limit, and if you’re interested in these types of questions, I highly recommend checking out Isaac Arthur’s youtube channel and backlog[1].
1) Most of them actually failed to achieve AI civilization during the process.
or
2) AI civilizations don't care about us, or have other means of communications that we have not achieved, yet.
You don't need to colonize anything for that to happen. The AIs can just sell tokens to each other.