>>34217750BW2 were pretty good because they had something for a lot of casual players. Some people only play Pokemon games for a new story, because they want that new experience. There was definitely a lot of new stuff to experience,but obviously not as much as a new region. Even then it was a great compromise.
Some new towns, new routes, new characters, sure some stuff was the same but it definitely was WAY more than any previous third version before it. And that was only possible because they made it a sequel, so BW1 didn't feel entirely pointless to own like SM does, or DP or RS.
Granted BW2 still had things I personally didn't like, like the protagonist designs and how some of the story was a little wonky. But overall it was a new enough experience in a region I liked to justify the purchase.
It's what third versions should've continued to be. All of SM was really screaming for a time jump for the next game, with the talk about gyms, or Alola becoming a more popular place because of the newly built League.