I guess I was wrong.
I originally predicted that Iris didn't want to return to Opelucid city because then Ash would learn she was the gym leader and her and Ash would have to battle together.
I honestly never expected the reason to be because she dropped out of the academy and wa afraid of what Drayden would say should she return.
It was nice to get some more background on Iris and (sort of) see how she became the person she is today.
I think their original intent was to have Iris be revealed as the gym leader but then B2W2 came out and they changed the whole thing.