of course it isn't the reason places look empty, but that's an exaggeration in of itself. the combine v rebel dynamic is always one that warrants careful consideration, and from a skim along the surface it doesn't seem that balanced. sure, you can't have the entire OTA flagged up at once but they still have a roster that rivals any faction aside from the CPs, and even then they're not that far behind.
4 months since the last OTA sweep? that seems unlikely. you just wouldn't need the faction so large if they were really being used that sparingly. i would be surprised if there are that many rebel characters who can obtain and maintain an equivalent level of equipment. i don't have the full picture of things, but i believe this is likely the view point a new player is going to have after skimming the forums and playing for a little while.
i would still stick with my earlier points regarding cps v ota, but i'm happy to agree to disagree there if the thread is going to die soon anyway