>>55945591A couple of things:
Players wanted to transfer their Pokemon to the GBA but couldn't. They also wanted a full national Pokedex at least accessible, but they didn't know FRLG were coming out. And even FRLG didn't have Johto Pokemon and players were mad they needed a Gamecube for Johto Pokemon.
Finally, the archetypal child, let's assume they were 7 in 1999 when Pokemon RBY were at their height in the West. In the year 2000 they would be 8. In the year 2003 they would be 11, nearly 12. They would suddenly be in teendom and think they are too cool for a 'kid's game'.
Plenty, and I mean PLENTY of people got bullied by gen 3 for liking Pokemon, because teenagers are dicks. Hence Pokemania dying by gen 3, until a new group of children could be 7+ when DDPt came out, and by then, Pokemania was dead and the series was very popular but not 'fadlike' in its marketing, and more of a mainstay behemoth in its vibe, like Disney or similar. This would carry on until DDPt and even HGSS which would be nostalgiabait.
There would be a slight, Pokemania like peak when GO came out.
By the time of BW and BW2, Pokemon had had a trough and would be the closest to a cult following such a mainstream franchise could ever have.