because they were never interested in a shared universe to begin with. labelling the universe gives people the idea that the stories are all connected, which they aren't, and it wasn't their intention. they wanted some movies connected to each other, sharing continuity, but not telling a story and not having one movie be required viewing for another. they're just DC movies, not "DC shared universe" movies. however fans and media labeled it the DCEU anyway, especially after BvS which seemed like it was trying to kickstart a shared universe (it wasn't, as we later discovered) , so there was no preventing it, people assumed it was a shared universe anyway (even after the countless times over the years that WB explicitly stated it wasn't their goal)