Expain? It is a different proprietary than the new series. While they may have the license to use the characters and the likeness and such of Kishimoto's work, they cannot do as they please with it.
Not only due to legality of it but rather the artist respect (community) for Kishi would go out the window if they try to use his characters all the time.
Remember, he gave his blessings to BORUTO series, not NARUTO series. That is why they cannot just simply make Boruto a Naruto S3. It has to be a different thing that branches off from the main material.