According to ComicBook.com, Warner Bros is reportedly the party that made the decision to replace Henry Cavill as Superman.
Warner Bros reportedly did not have another solo Superman project in the cards for at least a few years, which probably fed into the negotiations stalling and ultimately falling apart.
A source from the studio said, "Superman is like James Bond, and after a certain run you have to look at new actors." It seems WB agrees, and they will probably approach the Batman role with a similar outlook.