They are made that way on purpose because it has been proven that those "reaction face" thumbnails generate the most clicks. Unfortunately humans are like that. For the final form, check out the "Mr. Beast" channel's video thumbnails
He or someone else said they found a similar or better result with smiling instead of shock face open mouth so there are variations being pioneered. Think it was mrbeast talking about a new analytics a/b tool or might be confusing it with something else
The hilarious part is when they inevitably end up addressing it as “welp, we ‘hate’ clickbait thumbnails too but it gets clicks from dummy viewers like you all so we just gotta go with it because we got mouths to feed!”, as they post yet another video of them spending an absurd amount of money on some obscure eBay or Craigslist trash for content
