Since headline fonts are more expressive, and since there is so much to express in this crazy world of ours, there tends to be more of these fonts available, and because the expression is specific, they often have limited use. A designer might choose a particular font once in their entire career but regularly use text fonts for many different occasions throughout their career.
Headline fonts sometimes are expressive due to symbolism, such as a font made up of stars and stripes; sometimes they are pictorial. Historic styles developed throughout the ages can often be expressive of many things, such as invoking a certain period in time or simply an unusual display of elegance. Some headline fonts use a more direct form of expression, coming up with the visual equivalents of anything from a shout to a whisper.