I know. Oh, the tragedy of it all...
Sure, it was pretty much raped by the Yeerks and all that, but it can repaired, can't it? Imagine how great the ending would have been if Quafijinivon wasn't supposed to die in 300 days, but actually lived? The trees were created by his people, and with new Hork-Bajir, shouldn't it be easier to fix what had happened? Toby could have been the leader of it all. The final insult to them staying in Yellowstone is that, few people know this, but it's an active supervolcano. The last time it erupted was 600,000 years ago, and while it might not happen in this century, it could erupt any time time. Any time meaning any century within the next millennium. But imagine that, a new, strong, central colony of Hork-Bajir thriving well and prospering in Yellowsotne, only to be the first casualties when the darn thing blows up. One more generous contribution on behalf of the human race. Also, I agree, I certainly couldn't see Congress letting aliens joining them, and that was back in the days when Congress actually functioned as a collective whole that worked for the greater good. If it couldn't work when it wasn't filled to the brim with crazy, uncooperative, dysfunctional lunatics, then it sure couldn't work now.