Even though Justice League has yet to come out, pushing back the sequel in favor of Batman, a film that already has built up a lot of buzz, should work in WB’s favor. This will continue to keep Batman front and center as the DCEU moves forward, but also give audiences a chance to see Batman in a world after the events of Batman v Superman and Justice League. Joe Manganiello as Deathstroke should be a threat that brings Batman back to his roots as a crime fighter, instead of battling intergalactic threats, and doing this in between Justice League films should be better than doing it after.
As of right now there appears to be more interest in what Affleck will do with a solo Batman film than what Snyder will do with a Justice League sequel, which could be another factor in this decision. The reactions to the trailer for the first Justice League have been fairly positive and if the film delivers, there will be a desire to see what else is in store. Yet, this extended time between films will give them a chance to reflect on reactions to the film and course correct where necessary.
There is a lot of pressure riding on the shoulders of Snyder to make Justice League a movie that will be positively received, and in doing so, even more financially successful than BvS. But reports also came out after the post-production process of Batman v Superman that WB considered cutting ties with the director. The extra time between his as of now planned return will give all parties involved time to figure out what is the best direction moving forward. If Justice League is as great as people hope it will be, Snyder will certainly be back for a fourth time; but if more post-production issues arise and the film doesn’t hit, the sequel could be looking for a different director. Either way, fans of the DCEU should be happy to know The Batman is being prioritized and they should get to see it in the next few years.