The Snyder Cut was not an illegal, rogue action released against WB's authority, but sanctioned by WB. The heart of the movement wanted to see the legitimate production completed, not stolen footage cobbled together. Further, the Snyder Cut was the originally intended culmination (part one of it) of the DCEU Snyder established across several films.
Batgirl has no such weight behind it, as its a single, branching off story from the Flash movie, and there are some advocating the theft and distribution of footage all due to whatever they--alone--have told themselves about the merits of a film they know nothing about.