Just a lack of discipline on my part, really. I was doing well when I had a schedule for it of doing one chapter a week so I ensured that I didn't write 30% and then abandon it, wasting all that work. Now that it's 90-95% my brain just goes, I'll work on it after I've just done this, or that.
Most times I can wrap things up quickly because it's just a SPAG check, but this one is a proper rework of the first draft. Because of my frantic schedule, I basically just got the key points down on the page, lots of info dumping that needs to be worked into more active language and speech. The second draft just requires a lot more love, really, which means proper time sat down where it's the only thing I'm concentrating on.