Having a face on them is one thing. Sometimes the person is the subject of the video, and it's worth highlighting that in the video.

Having the person making the video staring at the camera, in a pose that says "look at how attractive I am" is another.

Also, this is not as hard and fast as you make it out. Here, I'll post some random examples in my feed:

• No face
• Indirect faces for a video game
• No face
• Face looking away, subject of video
• Not really faces
• Faces from video game subject
• Staring directly at the camera to make it look like some serious meta video, when it's really an April Fool's joke (this is the exception that proves how ridiculous it is)
• No face
• Faces, but the main focus of the video

In fact, I had to dig to find videos that would really qualify:

• Two faces staring into the camera, but they are properly framed and surrounded by the subject of the video
• Reaction shot face, but at least it's not taking up the entire frame
• Mutahar's mug behind his junky desk, but that's all of his videos and I wished he put more effort into his thumbnails and presentation

Even (most) of the female YouTubers on my feed aren't falling for it:

• Earlybird
• Maangchi
• Pushing Up Roses, besides the occasion "reaction face"
• CrystAAHHL, just to show that I'm not cherry-picking, yes, she does the reaction face way too much

Meanwhile, LaurieWired's entire catalogue is "look how attractive my face is!" This one doesn't even have the subject in the thumbnail! It's just her walking in a park. Also, what's up with her videos from two years ago? Did she completely change her makeup style just to look more attractive in thumbnails?