That could be because she was the original, and people love their nostalgia. Kasumi is the Japanese word for mist so Misty has a pretty deep connection to Team Rocket, in the West at least. There, he says that he wishes Misty was his granddaughter. Misty herself apparently inspired some edits.
Which is really creepy, but it actually gets weirder in the English dub.
Pokemon Go gets X-rated as characters pop up in players’ NAKED SELFIES
The gym leader side of Misty is my favorite side of her, because it shows that she's a strong and experienced fighter, and not just a '90s kid's fantasy. Misty and Brock always seemed to be playing mom and dad to Ash. A fresh take on sports: That could be because she was the original, and people love their nostalgia.