Why did they stop the series Fruits Basket?

The original (Japanese) manga finished because the story ended. I have no idea where the licensed english releases are right now, but it will sooner or later catch up and end as well. The anime ended because it followed a sort of different story-line as compared to the original manga source, though it could also be said that the anime ending was "open" since it really didn't feel "conclusive" and not all members of the zodiac appeared.