SECTUAL

In the thumbnails.

It gives the impression of YouTube being a place where people just endlessly flap their gums with varying degrees of annoyingly emotional fervent idiocy.

Probably some advertising maneuver born in a think tank.

"Smile really big or open your mouth wide for your thumbnails like
you're super excited about life and you'll attract more viewers because
most people are just moths and if you shine a fake light bright enough...."

It only gets worse from here.

they are fools , if a gypsy can see any of your teeth they will count them and each one takes a year off your life