I don't know where you're getting this idea from. Considering the cost to make this film, and that it's not an awards-bait movie like JOKER, they've been doing pretty good on the getting the advertisements for this out there. It's just a smaller scale, less money put into it movie. Kinda like Shazam. They're talking about doing sequels and spin-offs, with the possibility of Gotham City Sirens vs Birds of Prey down the line.
Just because WB obviously isn't looking to make a billion off this film doesn't mean they aren't invested. They have plans if it does well enough. They'll just use the rebooted Batman and a new Joker if they have to down the line, and not worry about the old Snyder continuity stuff.