The reason why seems pretty obvious as the ten that were announced were all related to the Justice League in some way.
A fan, however, was wondering why there was no mention of Sandman and asked creator Neil Gaiman on Tumbler about it.
Gaiman offers that Sandman is a part of the Vertigo slate of movies (which we can also guess would include the Guillermo del Toro Justice League Dark film).
Despite talk last month about the script being worked on, Sandman wasn't mentioned by name in today's WB news release of scheduled DC Comics films. There are previously mentioned release dates without film titles attached, so it's not clear if the status of the project has been altered or if the team at WB decided to focus their news on the easier to group together capes & tights titles due out. Has their been a change in the production timeline? Is Sandman going to be marketed differently?
NG: It’s not a DC Comics film. It’s a Vertigo film. That’s a different slate of films, and a different announcement.