It’s a stylistic flourish that he likes, many directors have similar “affectations” that aren’t as obvious (the angle of a shot, or a tendency to use extreme close ups or tracking shots).
A similar example: Quentin Tarantino’s obsession with close ups of feet, especially women’s bare feet. It’s a personal touch of both directors, though at least JJ’s couldn’t be misinterpreted as a “fetish”… Yet.