Many reasons.
1: The series is projected to outlive the Dragonball Series in length. It's already almost to 400 Episodes! Dragonball was 576 I believe. It's getting there.
2: It seems to remind me of D&D in many respects. The characters are just above average, they lose fights sometimes, there are things that can really ____ them up, and I don't know if anyone has caught on to this yet, but many of the Legendary Pokemon seem to resemble the Gods from the Realms on many parts. For instance, doesn't Lugia, who controls the oceans, remind us of Neptune, God of the seas??
3: I keep thinking that some day, Ash's Pikachu will evolve into something other than Raichu, and it will be on the level of a new Legendary Pokemon.
4: I also think Ho-Oh is preparing Ash for something.
5: Also, I truly do not believe, given the fact that they still make small references to it, that they have forgotten about the GS Ball.