It seems pretty likely to me that DC has changed its mind about how they want the series to intersect with the rest of their ever-changing plans for the rest of the line/continuity and that Johns/Frank have had to change their plans as editorial changes theirs. As posted already Frank has said he's not responsible for the delays. Johns isn't known for being slow but even if his film/TV responsibilities were getting in the way he wouldn't be this slow. There have been a lot of stories about summits between editorial, Johns, Snyder, King, and Bendis* to coordinate plans. Bendis didn't even come on until Doomsday Clock was well underway so these summits seem to me to be the only logical answer.
I expect we'll find out one day and I expect this will be the answer. I could be wrong.