That's not how it works lol
All they do is decreasing poly and texture res to the optimal amount suitable for the hardware(s).
Why not? Before the costumes had to work well for PS3/Xbox360 as well as PS4/Xbone/PC. So when they made the costumes they had to meet at the lowest common denominator, which was PS3/Xbox360 graphical capabilities. Now with the PS3/Xbox360 out of the picture they can up the polygon count and texture resolution. There's really no reason not to anymore.