Reasons this project was approved are considered as follows but none of them is definite: As population increased, shortage of food supply occurred; financial demand for national defense in remote regions occurred (in this theory some say enforced areas of the project were limited to remote regions such as Mutsu Province); it was a project to show off the power of Prince Nagaya (Nagaya no Okimi); and so on.
このような計画が策定された理由については、人口増加に伴い食糧不足が生じた、辺境での国防費に係る財政需要が生じた（この説では計画の施行地域は陸奥国などの辺境地域に限定する考えもある）、当時実権を握っていた長屋王（長屋親王）による権勢誇示的な計画だった、等が考えられているが、どれも決定的な説ではない。