I believe its because they A-B tested his thumbnails, editors found that they vacuumed slightly more eyeballs when he was smiling, and updated the thumbnail images of him not smiling with photoshop.
The fault isn't with the photoshop though, he just doesn't have a soul so it actually looks like that when he smiles.
This is somehow even sadder than "I have depicted you as the wojak".
"I contracted the least efficient computer possible to depict myself as the chad, therefore I win."