Aquaman just came out, so Aquaman 2 isn’t technically delayed, but it was decided to give the movie plenty of time to come together and be the best movie it can be.
There is a quote from Nintendo legend Shigeru Miyamoto that says “A delayed game is eventually good, but a rushed game is forever bad.”
That way, there’s a better chance for it to make the kind of splash that the first film did.
This is the philosophy that Peter Safran is espousing here.