Tradition

I think the original Pokemon for the Gameboy was a fine game for its age, but while the rest of the industry advanced leaps and bounds, Pokemon did some shy steps forward.
I'm not saying they should have deep, complex stories, branching skill trees, and real-time combat but I think they should not be lagging behind the industry and they should not be cutting features.
Still, the game sells, the fans buy it so who I am to fault them? What works, works, even if what works is doing very little work.