I'd like to pretend there was a good reason for these chapters taking as long as they did but there really wasn't (much to my editor's annoyance).
In fact it's been so long that the final chapter, 13, has actually been published, with the second and last volume due out in just over a week. From the outset I figured the series wouldn't necessarily be too long a project so it didn't come as too much of a shock, but I obviously wouldn't have complained if it had gone on longer.
At any rate 13 shouldn't take as long, I'll also check to see if the volume contains anything new (though chances are it won't).