What's with clip art?

Why is it that people feel compelled to use stock clip art in PowerPoint presentations? Is it a need to feel clever, that somehow the silhouetted man looking through the spyglass toward a star speaks of strong vision and achievement... is it a hope that it will divert people from the content of the presentation or from the speaker as they marvel at how that clip of art supports the story... How is it that clip art thrown on the page reinforces the brand, I simply don't understand.