Yep, about 2009 they started requiring bear canisters, with the exception of those that were doing climbing trips above timberline. The problem seemed to be that a couple of black bears figured out the free food opportunity at the several camp sites along the Thunder Lake Trail. Careless campers/clever bears.
But the story is more complicated than that. You see, many of the pre-2009 camp sites had ammo boxes chained to trees, which is where we would store our food at night. Then, the Park people decided to remove them. They told me that the chains could damage the trees, and that people tended to leave their garbage in them. I asked why they didn't erect pole setups for bear-bag hanging. Again, the reply was that the cross poles could damage the support trees, and that poles were unnatural. The guy also said that bear poles didn't really work, citing the Yosemite experience. I reminded him that poles were highly successful in Glacier and Yellowstone, and he stared blankly at me. I've become a sort of pest to the backcountry office, I think. When the head ranger sees me coming, he usually hides in his office, letting the volunteers politely handle my questions.
RMNP is run pretty goofy. They have about 30 black bears, which they're quite proud of. The thing is, at any given moment there might only be 15-20 actually inside the Park boundary, since there is a good amount of forested wilderness (ie-bear habitat) adjacent to the Park.
My take on RMNP is that they have chosen to spend a lot of money/effort on studying the ecosystem and resources, and also to cater to the day hikers. But they are proving to me that they really would rather not deal with backpackers.
And, yeah, I hate bear canisters too. It's OK though, as there are plenty of other good places around here to hike and camp.