Jennette McCurdy's mother recently died in September, 2013- and I mean, she's been through alot of stress. The certain *cough cough* pictures of her getting leaked, her mother's death, her career- everything. She's been through alot of trouble. I'm sure Ariana didn't want this to happen, nor McCurdy, it's just probably because of all the conflict. Through all of it, I truly understand.
The ratings were good. The real reason seems to me that Jennette was angry beyond control about everything and everybody. That resulted eventually even in publicly insulting her bosses and Ariana ("selfish leech"). Very unprofessional behaviour.
Ariana did yesterday the right thing to do is such a case by writing a letter to say thanks to everybody. She seems to be a more mature person than Jennette.
The tv show "Sam and Cat" was cancelled due to conflict related to the star Jennette McCurdy, including disputes about salary inequity with her co-star Arianna Grande and instagram photos that showed Jennette in provocative poses which is conflicts with Nickelodeon's squeaky clean image. Their ratings were good and weren't the reason for the show's cancellation.
This is a 20 year old woman, way too old to be on a kids show. She had trouble in her private life and things got leaked online which I'm sure made parents not tune in because she isn't a good role model. It was also clear that she wanted her music career to get off the ground.
I believe there was an internal conflict that caused the show to end in first place. There is a possibility that Sam and Cat were not getting along or that they didn't want to act together anymore. It had great ratings and kids loved it, but Jennette McCurdy did not want to star in the show any longer for personal reasons.
Nickelodeon show Sam and Cat was more than likely brought to end due to the conflict between the performers and producers. Much of this conflict was caused by the release of revealing photographs which appeared in the press in March 2014. No doubt these pictures caused problems for a TV channel primarily aimed at children.