Hi parttimeparli-
That's a good point - they shouldn't but they can. Frequently we hear that Presidents will handle this by saying something like, "I would entertain a motion regarding..... " and put the words and idea out there so another member can make the motion.
Lisa,
What you and the article you refer to don't mention is that: only members can make motions and that some members -presidents ( or the persons presiding over the meetings) and parliamentarians- shouldn't make motions.