but how did it hang on till 1996 (Why did they drag it out that long) and did they plan on season 11. they did close the series though with splinter saying he has taught them everything he knows.
Probably because the show had been on the air for five years at that point and it's original target audience who watched from Season 1 were growing up discovering new things and the current kids were more into things like X-Men and Batman: The Animated Series.
As for why the show lasted for another four years, I'm not sure, I think toy sales were still pretty healthy at the time, but apparently CBS cancelled the show because of it's lack of educational output so it was probably the Season 8 facelift of the show and lack of PSAs which let to it's end.