Because it should've been pulled off, in favor of something actually entertaining and good for younger children such as Dragon Tales.
The art design is unappealing, the character designs look completely juvenile, and not to mention Caillou himself, who is one of the whiniest and most mean-spirited main characters of a kids show I have ever seen. He whines whenever he doesn't get his way, he hurts his sister Rosie in many episodes (the first episode that features Rosie has Caillou pinching her, causing her to scream-cry), and he's overall a little brat. And the parents don't give him the punishment he deserves. The parents just calmly talk to him and tell him it's not OK, without any spatulas or wooden sticks to the a$$ or minutes in timeout spent. I mean, the infamous circus episode shows how bad this show is at teaching its demographic valuable lessons. Yeah, I know shows like Barney and Teletubbies aren't good shows, but at least they're so bad they're funny. Caillou is far from. It's hard to believe that this show came from the golden age of kid's shows. Oh well, that era wasn't perfect.