I think it is more that with Zack stepping away his vision was over. In truth JL was going to underperform even if Whedon doesn't put his version out because ZS was toxic at that point to everyone who wasnt a fan of his. (JL2 was almost a lock never to happen) His films were panned by critics and fans. WB knew the score and made a calculated decision to basically just end his vision and move on. In reality it was the right decision because the overall movie audience didnt want to see it. They decided to go more colorful, more ridiculous and smaller budgets. (outside Aquaman but that film blew up to make a billion cause Jason Momoa rules

) The results may have been smaller BO but the films were more liked by general audiences.
AT&T has a completely different view now though because they have a platform that can cater to a much smaller fanbase (they dont need the average moviegoer to like it) and still call it a success. Even though his films get panned and tend to underperform there is a very strong group of fans that really love his stuff. (not to mention a group like me that like them but are kind of over it and like the new directions more) AT&T realized they can have their cake and eat it too. They can still put the more "audience friendly" stuff like WW84 in the theaters and they can let the Snyder fans watch his version of Justice League (and I would assume BvS UE will be up there too as well) and that vision of the universe over and over again on HBO Max. No more competing with Marvel films (which the mass audience seems to enjoy more) now they can watch what they want and be happy with it. If it works, then it can continue.
It is important to note that timing is important in all of this. The Snyder Cut might be more liked now than before because people have a different sense of these films now. When Snyder made MOS, BvS and JL the darker elements of these films were not well liked. The masses (and the followers along with critics) only wanted 4 color Iron Man ripoffs. The films were not meant to delve deep into the issues...they were supposed to be Westerns with superpowers. Good Guys vs. Bad Guys (Batman being the exception always) with lots of jokey jokes to break up any sense of tension. Marvel made BILLIONS doing this. People who preferred a bit darker edge and more nuance were the minority. That has changed though. People seem more open to darker interpretations.
That doesnt mean the same critiques of Snyder's work wont be relevant or correct, but it might make the characters more palatable. MOS and its message about being an immigrant in America certainly has more relevance now than it did in 2013. Heroes falling from grace and rich egomaniacal businessmen destroying the world to prove their own greatness is definitely more poignant today. Maybe a Justice League where the flawed come together to fight an Evil Fascist is just what a lot of people need to see right now. If they can fix the issues in the stories (the holes) than these films could retroactively be way more important than they were when they came out.