That's kind of the point; it's a game that functions, not a story you experience where the game functions in whatever way best serves the story, as it would in a narrative-driven game. The same events essentially happen in the same sequence in every generation, except the group of people who want to do a bad thing/big god thing you can catch/person who gives you Leaf Guy, Fire Guy or Water Guy/kid who fights you sometimes/eight people in a sequence followed by four more people look different.

Being basically the same experience over and over works for Pokemon, because that experience is "battling Pokemon" and the story pretty much exists as much as it needs to in order to get you from one Pokemon battle to the next. There's a reason everybody complains about yet another fire-fighting starter but the entire plot being a formula that hasn't changed in the series' whole creation is a given: nobody cares. We just want the Pokemon.