Yes, my guess is that this is the result of a few food stylists or a single agency holding an opinion. It's not at all unusual as far as styling food goes, but maybe so for fast food.

I know that burgers are usually stacked to tilt away from the camera in photography to show the contents. (ie the bottom bun is laterally closer to the camera than the top in a downward view) I don't know why you would stack them to the side because it's more obvious, and in this case you can hardly see anything different at such a shallow angle. It's almost like they stacked them and then took the picture from a randomly selected angle or something.

BK is doing it in the very first one.

Honestly, it’s adorable and I love it.

It's to get people on social media posting about it so more people go look at it out of curiosity. Result is lots of people looking at the McD's menu.

Well, they've done it in a way that doesn't irritate me, so kudos to their marketing team.