It’s because their bodies are closer together in back, and perspective is a bitch.

Think of it like a triangle, the side of them furthest from us is the top of the triangle, their feet form the two bottom corners, one corner per person, and her body appears to be situated further back (based on her back foot being behind his back foot). Her shoulder is probably in his armpit. So since their bodies are close at the distant point, and the arm is the one closest to the apex of the triangle, it looks like it wraps around too far.