Why did High School Musical end all the sudden?

The High School Musical trilogy did not end all of a sudden. The series consists of three films: High School Musical, released in 2006; High School Musical 2, released in 2007; and High School Musical 3: Senior Year, released in 2008. The films were a success and were followed by two spin-off series, High School Musical: Get in the Picture and Sharpay's Fabulous Adventure.