Apparently Jason Momoa's 50-page treatment for the sequel was kind of dismissed by WB
https://www.menshealth.com/entertainmen ... interview/Momoa’s feelings about Aquaman—frustration, bitterness, apathy—are less about the character and more about how the character has been treated. “It’s not that I don’t care about Aquaman; it’s a wonderful character,” he says. “Aquaman is probably the hardest character in comic-book history. He’s made fun of and ridiculed, but I tried to give it heart and soul, and I’m proud of it in certain ways. Do I feel pressure for [the sequel] to do well? No. All I can do is give it my all. But it’s in a lot of other people’s hands.”
He’s referring to the turbulence of “different directors having different ideas of who Aquaman is” (Momoa has played Aquaman, aka Arthur Curry, in three other movies in the DC Extended Universe) and, more specifically, to the 50-page treatment he and Mendoza wrote for the sequel that he says Warner Bros. bought but did not follow completely. That bugs him and spins him into an impassioned, salty riff.
“That’s the reason why I love directing and creating. At the end of Chief of War, I’m like, ‘Yeah, feel free to knock, ridicule it. If it isn’t good, then we suck. It’s our fault.’ Yeah. I don’t wanna just go like, ‘I’m acting. I’ll be in my trailer.’ I love being able to burn for what I believe in. I’ve seen some of the most shocking acting performances firsthand and watched them edited, and they were amazing. I wish I could tell you who it was. I’m like, ‘What the fuck?’ I watched this guy who had to be fucking propped up. They read the lines to him. But this motherfucker killed it when the edit came in and was applauded for it. At that point, I was like, ‘Wow, this shit is made in the edit.’”