A curious thing about
Justice League is how it pretty blatantly rewrites the history of the DCEU.
I'm not talking about things like Victor Stone claiming the Mother Box that was used to reconstruct him only became active after Superman's death -- despite the fact that Batman v. Superman clearly showed that this was not the case. No, I'm talking about how they completely re-wrote Superman's behavior and how he was/is viewed by the people of Earth.
It was repeatedly claimed in Justice League that Superman was viewed as an inspiration to the people of Earth, and a source of hope. But pretty-much the entire point of Batman v. Superman was that this very-much was not the case: that Superman was viewed as a hero by some -- but most people were mistrustful of him, suspicious of his motives, and often resentful of his very existence.
Similarly, we can't say that Superman's new and improved attitude is a reaction to being restored to life, nor can we say that his much-brighter costume is something new -- because the "flashbacks" in Justice League showed that he had always had a positive and friendly attitude, and a brightly-colored costume.
So never mind that both Man of Steel and Batman v. Superman went to great lengths to demonstrate that Superman very-much did not have a cheerful and optimistic personality prior to his death, and that his costume was very-much darker than the one he wears in Justice League.
I'm guessing that this re-writing of history is largely due to the negativity that Man of Steel and Batman v. Superman engendered. If it means that Snyder and company have learned their lessons, then great. But I can't help but suspect this is really just a cynical attempt to re-write history on their parts, with the hope that most viewers won't notice.