Yeah they want anything DC film to be an event at the theater. Hence they cancellation of the HBO Max Batgirl film. Because it wasn't destined for theaters.
What I gathered, aside from the fact it was meant to be a made for TV movie, its a bad film and very much a CW pilot, so I'm guessing, if Warner hadn't been sold to Discovery, it would of likely been a pilot for a CW type show more a kin to Batwoman, the test screenings, were very bad and the new CEO of Warner, likely said "HELL NO, cut it, burn it, wipe it out completely!!"
As for Erza Miller, I honestly think he should be put in a padded room and dressed in simple, plain white clothes, he clearly not someone in their right mind and the fact Warner is keeping him on, is just stupid if you ask me, I think really Warner at this point, should be scrapping the film and wipe the slate clean and start over with the DC movies, the Synderverse is ok in some respects but, in general, its a huge mess because nothing was truly planned and for the first Flash movie, they are going Flashpoint, says, that they don't know what they are doing, because I think it would of been a better bet to tell the Flash's origins story in a film first, then do the Flashpoint, then again, I would of had the Flash & Cyborg origins stories told before doing Justice League, but as I said, they bungled things up badly, Marvel set down the template on how to start a cinematic universe, slow and steadly, which is how they became sucessful, with the first three phases, phase 4 is a walking disaster as there is no plan in play anymore and just a lot of useless noise!