The reality, is that it’s a Youtube algorithm thing. People are more likely to click on the video if there is a human face showing an expression. Surprise, shock, and anger, are all top picks to show on thumbnails. And, IIRC, the Youtube algorithm AI looks for a human in the thumbnail, and that will push your video up in the suggestibility algorithm.

And one other thing. It’s been shown to work really well with audiences that are kids, preteens, and teens. And being that that is the vast majority of users on YT… I think you can see the point of it.