Here's the interesting thing... Rugrats and Ren and Stimpy weren't originally going to be the big hits they thought, and Doug was the one they thought would be most successful. It was mildly, but it didn't get any merchandise of any kind until the Disney version.
And I honestly think had Ren and Stimpy not been so popular, it would have went down more like Angry Beavers or Invader Zim. They would have just fired the creator and ended it, instead of keeping it on and having increasingly bizarre (and not in a good, fun way, I'm talking crazy homeless guy in the subway saying scary things bizarre) plot lines and uglier and uglier animation.
But Rugrats was their baby... same thing they're doing with Spongebob now. They both climbed to popularity slowly... though I'd say Rugrats was more like Ed Edd N Eddy and became popular later on in the show's life. I wouldn't say KND, but anytime CN had a major hit, they ran it into the ground... did the same thing to PPG, until after the movie, and even then, when Craig moved on to Fosters. But it was like every day was a Rugrats marathon (again, knowledge being second hand, since I never had cable and had to beg the neighbors to let me watch Ren and Stimpy on Saturday nights for a few months).
Now Spongebob is their only thing, which is partially because they haven't found a new series that worked for a while. But consider the fact it's the only thing that isn't on Nick Jr they're running into the ground. I seriously want to see Tough Puppy (only because Butch Hartman created it, and FOP and Danny Phantom were great), but other than that, I could care less until TMNT... which, I hate to reiterate for the trillionth time, but I'm worried about.