They've seen with Top Gun that the market is there for big theatrical releases, and that's the vision with the new leadership, who is reversing course on the streaming strategy. They've recommitted to Henry Cavill and Ben Affleck, and both are getting another feature film (solo). They're pressing forward with Flash, in spite of Ezra Miller's bad publicity, because it's going to do crazy well in theatres (especially with the Multiverse Michael Keaton).
Batgirl did really, really poorly with test audiences. There's certainly an argument to try to recoup the costs by dropping it to HBO Max, but there is north of a billion on the line with the vision of this revamped D.C.E.U., and they'd rather shelve the $90MM as a potential tax write-off than potentially cheapen the universe they're trying to grow.