Of course a Marines change would have to come eventually right? This was the first arc where they were truly the main villains (Axe Hand Morgan is kind of a corrupt cop sort) so it felt the best to use.
The Marines in One Piece ironically have a vaguely Yakuza aesthetic with many of the Marine ladies looking like OLs (Office Ladies) The cloak really highlights their figure. Most of these sequences have dark implications for their arc but this one would complicate things so much I don't actually know if its darker than the actual arc or not?