Maybe they are just imitating the "smile" they see on their "girlfriends" faces when her other boyfriends come over?

The "ooh" face is what an adult woman affects when trying to convince a toddler that some new kind of food is really great, or a crayon drawing that the child made is the best achievement ever. Adults today remain infants and are ever conscious of the gaze of social media, and constantly seeking its approval. They unconsciously channel the behavior of their mothers, teachers and babysitters when they were at the physical age that corresponds to their emotional age. Something is good, and you want to draw attention to it? Reach for "Oooh" face! Posing for a picture to gain social approval? "Oooh" face!

It does not occur to them that "ooh" face looks like a chimp pant-hooting. Seriously, I hear "ook, ook, eeek, eek" whenever I see that face.