Pokémon truly died when sprites stopped being a thing. Since gen 6 all we've been left with are bland, cartoony 3d models that suffer from washed out colors and a lack of detail. Sure the 3d animations are fun to look at for the first 1.5 minutes but after that nobody over three years old really cares about them. Gen 5 did it the best when sprites had detail, vibrant colors and hit that sweetspot of having just enough animation to evoke a sense of dynamism.

When 3d models came along we knew this was going to happen some day. Gamefreak cannot just keep shitting out +-150 new Pokémon every generation and meet fans' expectations for the quality to remain the same, let alone improve.
If sprites were still a thing then all Pokémon would have made it into the game and we wouldn't be having this problem.