Yes I also experienced that (in 2.11.2 or something like that). Sadly this results in very boring games even on expert. Are you running 2.11.6 ? I remember it was said that it would be fixed but forget if it ever was.

When I reported it ,I mentioned that TR had similar issues before making the pockets of control for factions larger. However in TR the AI lusts for worlds no matter if player or other AI worlds, while in AOTR it seems the AI is configured differently to try to avoid attacking other AI. i.e. prioritizing the player.

I also wrote earlier that my theory was that the passive AOTR AI may be due to the AI having relatively small pockets of control and therefore it has problems forming combined fleets and invasion armies, this reasoning was based on the earlier TR behavior.

But I am probably totally wrong as I know nothing about the AI :)

In any case, if an AI pocket of worlds in AOTR has no frontier to the player and it avoids going against other AI it probably can just build but never (rarely) attacks from within that pocket. I say probably because that is a behavior I see sometimes but sometimes a pocket is practcally void of fleets (relatively speaking, maybe they have popcap 40 fleets or so) when I reach it after 100 turns with my popcap 300 fleet so not always.

This is all a shame IMHO as the AI can easily be exploited to not attack you by keeping a "buffer" world of one AI x planet (with one of your ships blockading it of course) between your planets and the AI y pocket. if I remember it correctly FOTR had larger pockets with more frontiers borderign the player and less neutral worlds between and in that mod the AI was also more aggressive (fun), similar to TR.

Give it time, they'll come for you.