The Kamisama Kiss manga is fully complete. It has covered everything the author wanted to convey, giving a comprehensive and fulfilling story. There are no loose ends or unresolved issues, making it a well-rounded manga series.
One reason could be that its distribution was limited. Another possibility is that there aren't many reprints, making it scarce. Also, it might be more popular in certain regions and less accessible elsewhere.
There are several mangas that share similarities with Kamisama Kiss. For example, 'Fruits Basket' has a touch of fantasy and romance like Kamisama Kiss.