Because I'm the queen of first drafts.
I just finished the first draft of my third novel. But instead of going back and editing right now, I'm starting the next book in the series. I did the same thing with the last two, and went back to edit later (still haven't entirely gotten around to editing the second one...) They're all from the same series, so I guess there's a part of me that wants to finish all the books, make sure everything flows well, before going back to edit.
I don't know how wise this approach is, but I think I'm going to stick with it for now. The next year of my life is going to be crazy with school (I am still a college student) and the possibility of me going on an 18 month mission for my church some time before next December. So even if I had a draft that was ready for querying, I wouldn't want to get on the publication road and then leave for that long.
So, since I know that publication is at least two and a half years off for me, for now I think I will go ahead and finish the first drafts of all five books in my series. That way all I have to do when I get back is edit--seriously edit.
What's your approach to writing a series? Do you like to plan everything out before seriously editing, or do you go book by book? Does it vary by series?
Get excited for the Olympics!