I've been a Pokémon fan for over 25 years, and I've got a lot of love for every generation. As much as I don't like to admit it, I'm old enough to remember the rough transition from Gen 2 to Gen 3 without any rosy veil of childhood nostalgia. Here's my take on what made so many players leave the fandom post-Johto.
Edited to add: Wow. I've never had a video get this many comments before, and I'm struggling to follow my normal policy of replying to every one. (I'm also vacationing with my family atm, which makes it trickier.) I'll monitor comments, and although I won't be able to reply to many (at least not right away), I really do appreciate hearing everyone's thoughts!
Finally, since I was vague about it and it seems to be causing some confusion: I was in high school during Gen 1, not elementary. I drove myself to events and meet-ups and was as much a part of the community as I could be without the magic of the modern day Internet. These are my recollections and experiences, and they come with a heaping helping of YMMV.