If one wants to publish in the most famous manga magazine in Japan, and therefore the world, by accessing a huge pool of users, a budding mangaka must inevitably sacrifice something. In the case of Weekly Shonen Jump, it is relinquish part of the rights to their own serieswhich can be managed by the publisher.
All new Weekly Shonen Jump manga will be owned by Shueisha, who can benefit by creating merchandise and derivative works. The writers also own some of the rights, but it's still a partnership with publisher Shueisha holding most of the power. This happens with all titles, even those by very famous authors like ONE PIECE and Naruto, it happens to all but one: Hunter X Hunter.
If you look at the rights lists of the various manga, you immediately notice how Hunter x Hunter is the only manga whose rights belong exclusively to the author and not by Shueisha. Yoshihiro Togashi managed to wrest a very special agreement from the publisher, a practically unique agreement that hasn't been granted to any other mangaka, not even Kishimoto with Samurai 8.
How Togashi got the rights to Hunter x Hunter is not known, but what is certain is that this particularity will not allow anyone to get their hands on the manga unless it is the will of the same author. Author who returns to drawing, among other things, as can be seen in the recent tweets related to the chapters of Hunter x Hunter.