The word franchise is used a) way too often and b) totally incorrectly in gaming. Look at the Wikipedia listing of video game franchises. Most of them are simply series of games.
A franchise is an IP with a) multiple sequels, b) spin-offs, c) adaptations into other forms of media and d) merchandise. Take Mario. On top of the original 2D and 3D series, there is the Party series, the Sports games, at least three cartoons, a feature length movie, comics, toys, playing cards, trading cards, lunchboxes, and even a damn cereal.