I believe it was their way of downsizing for the years to come. As I recall I think 1976 was the last year for the Gran Fury. I also seem to recall they stuck the Fury name on the Diplomat a few years later.
But then again if you've ever noticed, in 1977 I think it was, the Road Runner name went from being on the Satellite to the Volare.
Crazy stuff going on at the Chrysler plant for sure.