It's really not.
People claim that WB took risks with the DCEU. They made poor decisions, but from an executive point of view their plan is very obvious and very safe.
The biggest success they've had with superhero stuff is with Batman. So when Green Lantern was a failure, they thought "he wasn't dark enough" and you can, to this day, google the articles from the producers of that flop where they promise that Green Lantern 2 will be darker and edgier.
And that's because WB puts all their eggs in the Batman basket.
Man of Steel is controversial and criticized? We need Batman for the sequel.!
What else can we do? How about a suicide squad movie? Fill it what Batman villains! And Batman can cameo!
Justice League? Sure, so long as Batman can be the one to get the team together.
Nightwing! Teen Titans! Batgirl! Harley! Give them all movies! Joker can get three!
Wonder Woman? Is there any way we can get Batman in there? As a framing device? Great idea!
Flashpoint is the choice first and foremost because it's a Flash story that has Batman all over it.
Because when all you have is a hammer, everything looks like nails.