I almost have the feeling that Carell, Novak, Krasinski, Fischer, Wilson, and Kaling are all ready to move on, and dont want to drag things on and degrade what they've done. The success they've had with the series; coupled with what Krasinski/Carell/Fischer/Wilson have done in movies and Novak/Kaling writing, probably means they will want to work on what they want to do and not necessarily keep writing for The Office.
just my 2 cents, but 7 (very successful) seasons from a britcom that had all of 14 or so episodes is a nice accomplishment. They've done well and deserve to go out on a high note without NBC riding them for an 8th or 9th year.
Edit: Forgot Rainn Wilson. Added.
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