Of course, there is not a reason why the manual page cannot have images and figures. The whole PIC language exists to put diagrams into things like ?roff, and it was at one time de rigueur to format the manual pages to postscript and send them to the printer. It was also common in later times to generate PS or DVI output and view that with the appropriate viewer. Honestly viewing the manual pages with a plain text pager is the new, worse-is-better method.