The first two generations I think were relatively close to each other in terms of release, at least in the States, but both came out when Pokémon's popularity was a cultural phenomenon and then there was Togepi's introduction in the anime, so Johto has always been fresh in a lot of genwunners' minds. G/S/C having Kanto post-game (as well as having the Johto region be included in the OG Pokémon series for anime-only fans who eventually fucked off after Misty left) may have helped.
Johto's always had its share of criticism, though, and they're not unfounded. Gen I at least had exploitable glitches and bugs that captured the imaginations of kids everywhere, Johto's only commonly known glitch is, what, the cloning glitch? I know it has its own share of issues, but Missingno. was rather special.