According to the BBC, the film "tested poorly" with audiences. How much of a stinker does a film have to be for this to happen?
I recommend the Hollywood Reporter article. This is ... more complicated.
Fundamentally, the issue is that the movie is both too expensive and not expensive enough... which, woah. But here's the basic gist-
Warner/HBO used to be a part of the Big Blue Ball of Death (AT&T). Now, that wasn't a perfect situation, but it meant that there was a of money flowing from AT&T to the subsidiaries to make movies and put lots of cool streaming stuff on HBOMax. Which showed- I mean, HBOMax was just churning out content. They also led the way in having real movies on streaming during COVID.
But then, disaster. AT&T sold off the HBO/Warner parts to Discovery, and now we have have Warner/Discovery. Except that the Discovery people were put in charge. And they don't have a lot of cash-flow. They've been looking for over $3 billion in savings.
Which has led to the following-
1. Brain drain as the HBO/Warner creative have been leaving.
2. Massive cancellations of projects. Everything from CW shows to HBOMax shows to TNT shows to movies in the pipeline.
3. A decision to "re-focus" on movies for theaters as cashcows, instead of the longer-term play on the streaming service.
So what happened with this? Well, it was originally going to be a "big budget"
streamer release- straight to HBOMax. But here's the thing- the new powers that be don't want to "tarnish" the DC Superhero movie universe by releasing these movies straight to streaming.
So ... why not just release it in theaters? Because it's "only" a 70 million dollar movie. It doesn't look as awesome as a big-budget tentpole movie should. And it would require extensive CGI and reshoots to bring it up to that quality ($$$$) as well as a massive marketing push (even more $$$$$) which Disco-Warner doesn't want to spend.
Which leads us to the position we are in now- $70 million up in flames.