One of the problems with that show is Zooey Deschanel. They reworked a lot of storylines around her being pregnant and those storylines were better when she wasn't on the show. When she returned, the show was noticeably worse.
New Girl was super good when it first came on but after season 3... erm. It's just been a downhill slide.
The ratings are terrible now and 8 episodes is good... put it out of its misery. Likely, they would have liked to have end the show at season 5 or 6, but the show was contracted and the money lost if canceled (payouts on contracts) would have been greater than just letting run on empty like it has.