As I've been saying, if you have 15 episodes worth of important information and 12 episodes to air it in, somethings gotta go. If an editor says they need a story that is 300 pages and they get a manuscript that's 450 after they edit out all the extra parts, that's a failure by the author not the editor. If they still have to use that story and cut it down to 300 pages, that's still a failure on the author, the editor just had to deal with it.
While they might have an unlimited budget, no one wants to waste money. They, and the channel airing the show, dont want to spend money buying an extra season's worth of time slots for less than a season's worth of content. Double episode aren't an option either, as other shows have already contracted for those time slots.