>>49489231It was just a time thing. R/B/Y came out when I was 7. It was the biggest thing going. G/S/C came out when I was 9 and even more people were playing it since everyone got a gameboy colour, every single person knew about the franchise at this point and g/s/c had even more to do. But then ruby/sapphire didn't come out till 2003. I was 11 by then and a lot of other players were now teenagers. Tastes changed and a lot of kids were now into other things. Pokemon was essentially seen as a baby franchise at this point. Heck, I was into pokemon in a massive way as a kid but I didn't even know they were making a third generation of games until I saw a big poster for sapphire. Thought it looked like shit and kyogre looked like a digimon. Yugioh was also massive at the time and competing for interests too. Honestly in the late 90s you were spoilt for choice as a kid for things to play and watch.
It also killed the appeal for some that you couldn't bring your pokefriends from G/S/C over to R/S/E.
As for pokemania's second wave, just time again I guess. X/Y and GO were massive but that's about it.