Given the following context:  The film begins with the Descendents' origins in the neighboring communities of Hermosa Beach and Manhattan Beach, California in the late 1970s. Middle school friends Frank Navetta and Dave Nolte start the band in 1977 by writing songs together on guitar. Classmate Bill Stevenson impresses them with his musical talents and becomes their drummer. In 1979 they meet bassist Tony Lombardo in Long Beach and recruit him to the band. Nolte bows out to join his brothers in The Last, and Navetta, Stevenson, and Lombardo record the Descendents' debut single. Stevenson's high school classmate Milo Aukerman joins the band as lead singer, and the new lineup builds a local following through their catchy and melodic songs, energetic live shows, and Aukerman's image as a nerd. They release the Fat EP (1981) and their debut album Milo Goes to College (1982), so named because Aukerman leaves the band to study biology. Stevenson drums in Black Flag for the next few years. In 1985 the Descendents reconvene for a second album, I Don't Want to Grow Up. Navetta has burned all of his equipment and moved to Oregon, and is replaced by Ray Cooper. Stevenson pushes for the band to tour, but Lombardo declines and quits. He is replaced by Doug Carrion, and this lineup records 1986's Enjoy!, after which Cooper and Carrion both leave the band. Stevenson recruits bassist Karl Alvarez from Salt Lake City, who brings in his close friend Stephen Egerton to play guitar. The new lineup releases the 1987 album All, themed around the philosophical concept of "All" invented by Stevenson and friend Pat McCuistion. Aukerman leaves the band again to attend graduate school.  answer the following question:  Why did Milo leave the band the last time?
to attend graduate school.