>>34121194It's a matter of control in some cases. Artwork posted on the artist's account can be taken down for whatever reason if the artist needs it to be, while they can't do that to the same artwork posted somewhere else, especially if the signature and source is left intact. This is particularly prevalent among Japanese artists because Japan's copyright laws are actually quite strict and if the rights holder decides to go against an artist for some reason, the artist has more to lose. Some artists work in studios or as assistants or similar, if their employers disapprove of them posting fanart of what is their creative property, they can lose their jobs on top of fines.
Another issue is if the signature and source is removed, then that exposure goes nowhere.
