River Country was a casualty of the popularity of bigger, better, more technologically enhanced water parks. As much as some people loved it, more people loved the newer water parks, so much so that they were far more profitable to operate.
As far as the location, we can only speculate. I for one am happy that they didn't build a humongous water park not far from my timeshare at Wilderness Lodge. I think it would have made that area too crowded, especially the roads.