That is a good question! The simplest answer would be that it is a story-arc universe like the New 52 or Rebirth comics but in the form of movies. As for a more vivid description, I think the DCEU has a really intense realism that makes it believable like these things could actually happen. I personally find it a bit more realistic than the MCU in that the heroes are dealing with more realistic problems, especially Superman, but that is not noticed as much because the main story of most movies focuses on a ‘big baddie’ who isn’t an everyday problem. But in the background and in-between shots you can see the heroes dealing with things like floods, small crimes, construction accidents, train derailings, and I could probably list more if I had my notes open, not to mention that when was the last time you saw a hero in court answering for their acts? The DCEU’s progression over events over time is well laid out and ties in a lot of unique places/instances so there is no stone left unturned or question unanswered while still leaving a lot of room for headcanons and fan theories. There is a lot of subtle hints going on that build up a bigger picture, and that’s my favorite thing about the DCEU, discovering all those little hints of other everyday stories occurring besides that of the hero. Thank you for your question, I hope I was able to answer it to your satisfaction!