They felt that 6.x resulted in the transition to Dawntrail being weak, which is why they went back to the x.3/x.4 split of story that they used to do.
I've been saying this all along. A very large part of DT's pacing issues (and why Wuk Lamat had to be in right up in your face every second) was because the Zero story took up all five EW patches. DT didn't get the EW .4/.5 patches to do all the initial prep. Instead, the DT leveling MSQ had to waste a HUGE amount of time doing very basic setup and characters introductions and stuff, that in any other expansion would have happened ahead of time.