Why was Joan Rivers banned from The Tonight Show?

Answer 1

Johnny Carson felt Joan had stabbed him in the back when she got her own talk show on FOX. Evidently, he felt she should have told him personally that she was getting a show but he claims she did not although as she told the story, she did inform him but he felt she should have asked his permission, but she never understood why exactly he cut her off so completely.

The ban continued under Jay Leno's hosting stint since he thought it would be disrespectful to Johnny's memory but it was lifted when jimmy fallon invited her on his first show & then again on a later episode.

Answer 2

Louise Lasser was in the middle of a drug abuse problem and during rehearsals, she crawled into various offices at Rockefeller Center. She insisted on appearing in the sketches solo or with Chevy Chase only, and on the live show, she rambled and was a complete mess.