Can someone explain promotional photos for TV shows and movies?

This is what I am referring to.

How and why did this type of thing start? I don’t understand it at all. Don’t tv shows want viewers to buy into the show? When we watch a fictional tv series, we have to suspend our disbelief and completely buy into the characters. These types of photos, where everyone is posing and looking right into the camera, seem to be designed to shake you from your immersion in the series and remind you that it’s just a product. They’re a bunch of actors, and they look like complete jackasses when our corporate marketing department forces them to pose for these overly-shopped photos.

I don’t get it. Maybe there is some reason why it is done.