Jason Alexander threatened to quit Seinfeld amidst concerns that his character, George Costanza, wasn’t receiving enough screen time. In his upcoming memoir, Entrances And Exits, Michael Richards revealed that Alexander was upset with the network and showrunners during the show’s third season in 1991. Richards told outlets that he accepted being sidelined from an episode with grace. However, Alexander was allegedly greatly displeased with the situation. In his memoir, Richards wrote that Alexander was under the impression that he would be one of the show’s main draws and thought his screentime…