[jocon307]

"My best guess is that they do that on purpose, in order to force the viewer to spend more time looking at the ad, trying to match the names to the faces."

Yes, that's probably it. Here I am still thinking about all those movie posters from the past, which otherwise I would have forgotten.

[wogawoga]

It's actually based on billing. Here, Kerry would be getting top billing and therefore be first, then Edwards, and Mcawful last. The order they appear in the image doesn't matter. (Spent a year doing layouts for Sony Pictures.)