why did ozzy leave black sabbath

Ozzy Osbourne left Black Sabbath in 1979 because he was fired by the band members due to his excessive partying, drug and alcohol use, which they felt was hindering the band's ability to produce quality music. The band's guitarist Tony Iommi, bassist Geezer Butler, and drummer Bill Ward collectively decided to remove Osbourne as he was becoming unreliable and was often absent or incapacitated during crucial studio sessions. This decision was framed as an ultimatum; either the band broke up or they carried on without Ozzy. Despite Ozzy's claims that his substance use was similar to the others', the band felt they had no choice but to let him go to continue making music. After being fired, Ozzy went on to have a successful solo career. Later, he and Black Sabbath reconciled for tours and reunion projects, but the core reason for his initial departure was primarily his substance abuse issues impacting the band's work.