I can't say, but I did notice this too. I was recently playing one of the larger campaigns on admiral difficulty (or whichever is max) because I hoped it'd be more of a challenge. It wasn't. Playing IR, you can basically zerg the board. Just put Isard in a fleet with a few frigates and a capital ISD or two, with a few cheaper starting units, have 1 unit jump in, wait for map fog to clear, then jump in Isard and the rest right on their space station. Then leave a space unit behind to prevent them from building it up and rinse and repeat. In the early stages of the game, I'd say consolidate as many ground troops into an army and zerg those planets before they have sufficient time to fortify. but anyway, I'd cleared out all the space stations within my 'borders' established a few front/chokepoints and captured numerous planets before the AI had the time to build them up. I was attacked by Hand three or four times, but the only time the NR has attacked is some pitiful attempt with 10 ships.
Where I am now is I control about 70% of the map (with about 5 areas just controlling the space above enemy planets). I haven't really even pushed out into Hand or NR territory proper, I just secured and unified my area. I was looking in the 'economics' information and NR had upwards for 7 million credits, while I had only about 230k in reserves and basically, except for a 20 to 30 Tie Defenders, was only fielding the space troops I'd started with. less a few lost to Hand. And I haven't even lost a single starting planet. NR hasn't done shit despite having something like 30X the credit capital, and aside from a few thrusts from Hand (who has 15x) which I repelled, they aren't attacking at all. I actually forgot to pause the game, went downstairs, grabbed a drink, made a sandwhich, came back up and realized game wasn't paused for like 5-minutes and there were no attacks. And I'm pretty sure I've actually cut a swath across the map early on that divided the board so they can't attack anyone BUT me.