For some time, the DC Universe has been in a constant state of flux. While James Gunn has been working to invigorate Warner Bros.' superhero vision with new movies like Superman: Legacy and Batman: The Brave and the Bold, the old DCEU still had films in production to put out. Andy Muschietti's The Flash is a prime example, with the final film closing out that past era being Aquaman and the Lost Kingdom.
Source:https://www.cbr.com/aquaman-2-trailer-spoiled-aquababy-fate/