Who draws the good diagrams for the motivation of an article I see some papers (more specific Magazine, Tutorial, and state-of-the-art papers) contain good illustration to highlight the motivation of the article. It's not about simple flow chart or block diagram with notations, however, some extra effort that makes a paper more exciting. Is there any professional team (e.g., journal's editorial team) to make these type of illustration or do the authors themselves draw it? I feel that art and science are not really far apart, rather they are combined.
The illustrations that are included inside a journal article are essentially always created by the authors.  This may entail getting somebody else to do the actual graphics work, if none of the authors are skilled in that area, but the design concept is created by the authors.

In some higher-end journals, some articles may be specially highlighted (with graphics about them appearing on the cover, for example).  In these cases, the graphics are typically produced (or at least heavily edited) by the journal's design staff.  The authors are involved in decided how best to illustrate their work, but the journal professionals create the actual images.