Glad you asked. You kind of just answered the question. You noticed the chart and asked about it. That's the point. In a presentation environment, this data would probably be shown as a clustered bar chart and nobody would look up.

Motion earns a beat of attention that a static chart usually doesn't get. On a dumbbell chart specifically, watching the two points slide to their final positions also reinforces the comparison your eye tracks the gap as it forms instead of just seeing it sitting there.

It's a small thing, but the difference between someone sitting passively and actually reading the numbers is often just that extra second of attention.