Ezra was only in Justice League. That’s it, 1 appearance as the Flash. And that movie bombed. So not surprising audiences didn’t really care to see a whole movie about him.
Add on to the fact that it was Zod again, who audiences already saw in MoS, which had a mixed reception at best. So as a villain, I don’t think it was enough to draw audiences in.
The only real hook for this movie was seeing Keaton as Batman again. But for people like me, the negative outweighs the positive that I’m willing to wait to see it on Max later this year.