>>58258303That wasn't G/S's fault in the slightest. That fell on R/S. Not because the game was bad, but the move from GBC to GBA (having to get an entirely new handheld) with zero ability to transfer from GBC to GBA ruined the series for a surprising number of people.
Also the generation of kids who grew up playing the GBC Pokemon "grew up" into their edgy "lol nerd you're still playing Pokemon?" teen selves which also hurt its popularity. Japan was entirely unaffected by this, but this shit was all over the west.