Plot hole: The whole plot of the first "Brother Bear" was that Kenai had to go to that mountain to become human. But at the end of this movie, the spirits were about to change Kenai back into a human in the middle of a cliff, which makes the entire first movie completely pointless.
Plot hole: Kenai getting bonked on the head with a pinecone at the end could never happen. When Nita walks over to Kenai and Koda, we see that the only trees are to Nita's right. The pinecone then falls on Kenai's head from ABOVE. They look up and see a tree above them. Cut to a wide shot, there are no trees around them.
Chosen answer: Probably for just that reason - they were waiting for the right moment to change Kenai back.