The fact most people go "Will Smith's son" like you did. It's not enough to just be the 'son of' and get butts in seats. Jackie Chan is a recognized name for sure but it doesn't mean his ability to get tickets sold is that great. His films aren't sold on his name alone. Look how many "buddy films" he has to do. When is the last 'starring Jackie Chan' film that lit the box office on fire?
More people will likely see Karate Kid with
Chan than a Kung Fu Kid with Chan based on some recoginition of what they can expect with the known quantity of Karate Kid.
Before you say it I know that Kung-Fu kid should
give the same conotation to people but frankly the longer I'm around the more I realize the mass public doesn't connect those dots as easy as we do.