Except that they don’t want to. The two halfs format, which is partly to be blamed, have been criticized a lot, but they kept saying that that’s what works best for them (because that way they can just write 11 episodes and just forget about them and do something new and unrelated to the overall narrative of the show. In other words, that allows them to be lazy). As long as they keep the two halfs format, they will never allow characters to be properly fleshed out, everything will be contrived just to finish it fast and move on to the next shiny toy.
See I feel like the Pan arc, which was the first time they split the season into two halves, actually didn’t assassinate the characters. I think that arc proved it could work. The whole reason they decided to do it this way was because season 2 ran into a huge problem with big “filler” episodes and unnecessary material. There are parts of season 2 that dragged. They felt they could tell a more concise story splitting it up and I can’t blame them for wanting to try something new. Unfortunately, a consequence of doing that, has been focusing a little TOO much on plot and not taking a breath and giving us much needed character development scenes and more consistent decision making. But in no way do I think they started splitting the seasons so they could deliberately forget about characters and do something unrelated to the narrative. I think they saw the flaws with season 2, and thought this would help concise the story a bit, and many fans, myself included, thought this was a good idea at the time. They just unfortunately have lost their way since the Pan Arc when I felt the half season worked well.