https://screenrant.com/cheers-ted-danson-unhappy-end-of-show/

Emma Thompson, who memorably guest-starred on Cheers as Nanette Guzman, candidly looks back on the unhappiness of lead actor Ted Danson.

Unless he had a 10-year contract, he just had to do what Shelley did: leave. I know he made that decision after season 11 (which ended the show) but he could have left earlier if he was unhappy.

Life's too short to stay somewhere you're unhappy.