Maybe because they are easier to sit around in and you dont have to worry about flashing others when wearing them
In an interview with the Los Angeles Times, costume designer Amy Roberts revealed that she and her team had to get permission from the original wedding gown's designers, Elizabeth and David Emanuel, to reproduce the dress for the show
The derbys open lacing system makes it a little less smart but a better fit for separates like an odd jacket and trouser combination

Shop more Designer Christmas Party Outfit Ideas selected and reviewed by our expert fashion buyers and stylists RACHEL GILBERT Ochre Ruched One-Shoulder Bubble Hem Mini Dress $795 ALICE + OLIVIA Retha Strapless Maxi Dress with Godet-Pleated Side Panel $595 SAINT LAURENT Open Back Velvet Skater Mini Dress $4,250 PATBO Lurex Tulle Bustier Midi Dress $895 ISABEL MARANT Daphne Dress $1,590 HALSTON Sya Deep V-Neck Sequin Midi Dress $495 LOVESHACKFANCY Ganette Velvet Mini Dress $345 RETROFTE Jeanette Strapless Lace Dress $678 MAC DUGGAL Strapless Bustier Net Gown With Spiral Ruffles $498 NBD Rosabelle Midi Dress $258 TULAROSA Naiya Mini Dress $358 LOVERS AND FRIENDS Mary Kate Mini Dress $228 ASTR THE LABEL Pleated Bustier Midi Dress $99 HELSI Leslie Strapless Sequin Midi Dress $495 MAEVE Puff-Sleeve Keyhole Embroidered Mini Dress $178 FOR LOVE & LEMONS Della Mini Dress $198 MORE TO COME Malia Mini Dress $82 SUPERDOWN Abigal Mini Dress $78 AMANDA UPRICHARD Magnolia Maxi Dress $299 VERONICA BEARD Bixie Stretch-Silk Slip Dress GABRIELA HEARST Immanuel Strapless Wool Maxi Dress $2,750 SIR

Short sleeves, self-fabric sleeve cuff detail
Get the look: style GL2016 | Strapless Sweetheart Soft Mesh Long Dress with Sheer Back 3