If I were to picture Arthur's animation to change, I would have thought Between the Lions shorts. But I'm glad that they didn't go in that direction.
I assumed that Arthur would stop with at most six seasons because usually PBS's animated series last no longer than that while the live action ones (Sesame Street, Mister Rogers' Neighborhood, Reading Rainbow) last for decades.
There are two animated kids' shows that I know of that have ran for almost as long as Arthur: SpongeBob SquarePants and Pokemon. I don't know whether the original viewers of those shows are getting tired of them or not.