"As part of our DC slate, some legacy development titles including New Gods and The Trench will not be moving forward," Warner Bros. and DC said in a statement. "We thank our partners Ava DuVernay, Tom King, James Wan and Peter Safran for their time and collaboration during this process and look forward to our continued partnership with them on other DC stories. The projects will remain in their skillful hands if they were to move forward in the future."
Ava's got lots of other projects lined up, including a CW DC show, so I'm guessing it's more of a time commitment thing. James is still doing Aquaman 2 later this year.