I think you've got it backwards... He's the most popular Pokemon in japan, that's why he got the ridiculous form XD
There was also a poll on The Escapists site, where they asked people about their favored starter, and Frokie was chosen by 50% of the poll voters. And not to mention that he was already super popular in japan even before the anime.
Also, He's a ninja and ninja's are cool... which makes him easier to market to the younger fanbase. He's also notorious for being one of the best sweepers in singles in XY, so he's also popular with the competitive crowd. Even when we disregard the anime, It's easy to see how he rose in popularity.