You can only get the super rod in B/W2, and you can only get it after the e4 and champion. Why is there only one type of rod and why is it only obtainable at such a late stage in the game?
What I realized is that the Gen V games are kind of different than other generations. Only game freak would know, but my guess for Black and White is that the Pre National dex has only Unova Pokemon, so there would be a limited amount of Pokémon to catch before the main story.
Hope I helped!