>>36852592Because despite the anime's earlier seasons, she wasn't well characterized compared to other Pokégirls in the anime or games and even as far as fap material goes, other Pokégirls just satisfy tastes Misty can. Flannery has bigger tits, Elesa is tall and blonde, Hilda's also a tomboy but built like a truck, Whitney's got a sweeter personality, et cetera.
Misty still has a place in our hearts, be it nostalgia or aspects about her designs in general but the fact remains is that as the series expands there's just other characters that have more distinctions and/or appeal that Misty just doesn't fulfill. That's all there is to it.