Well, they haven't been added *yet*. The KotOR 1 characters were added well after the game's release and is probably the same deal here.
Regarding to grown people, I think that they *had* to accept adults because with all the darksiders popping up, they can't just send kids to battle these guys. After a while I think Luke will go back to accepting the bear clan, however I don't know much of the post RotJ events other than the Jedi Knight series and Yuuzhong Vong deal.