We're not talking popularity here, but size, physical size - er, scope. Distance! Get your mind out of the gutter.
Mike Newell directed 2005's Harry Potter and the Goblet of Fire and the upcoming Prince of Persia film. When asked about the difference between the two, he told website Latino Review, "It's bigger because Harry Potter in the end is bounded by the school. You don't really go outside the school."
Obvious difference! (Though, Prince of Persia: The Forgotten Schoolbooks sounds intriguing at the very least.)
Following that up, Newell said this about the Prince Persia film: "What you're doing is ploughing the field for the very first time, but with Potter, the field had already been ploughed."
Prince of Persia: The Sands of Time will hit cinemas this May. It will not take place at a magical British academic institution.