Quoted By:
I think Dawn just came at the right time. She was the third female lead coming after Misty and May, and after everything the writers learned giving May her own goal and spotlight, they went full force with Dawn right from the start smartly making her a co-star. I do think Piplup's popularity caught the writers by surprise though since in early DP, Piplup did stay in its ball for the first 40ish episodes.
Besides that Dawn came during the 10th anniversary of the franchise, so a whole bunch of younger generation of kids were getting into Pokemon for the first time after the first 10 years of the franchise had a lot of original fans aging out of it. Then the decline in the animes ratings for the whole 2010 decade is why a lot of the other groups didn't quite reach the same mainstream levels of success.
