Why was new adventures of old Christine cancelled?

There's no TV show called "New Adventures of Old Christine." It's likely you're thinking of the popular sitcom "The New Adventures of Old Christine".

The show, starring Julia Louis-Dreyfus, ran for six seasons from 2006 to 2010. It was not cancelled.

The show ended its run naturally after six seasons. The creators decided to bring the story to a close and felt they had told all the stories they wanted to with the characters.

There were no ratings issues or behind-the-scenes drama that led to the show ending.