I wonder if a part of the reason that the video is powerful is in that it actually agrees with me, at one level. Why did they do it the way they did it? Why a person, particularly a young, masculine, strong, attractive person, telling you that you're amazing and that you're loved?
I reckon it could be because instinctively the creators understood that human value is bestowed. That's the power of the video. It forms a relationship between the speaker and the listener. In their eyes, you are awesome and therefore, you feel a sense of worth bestowed by that relationship.
That's why it matters who did the speaking. Would the video have worked if they'd cast this guy?