Whenever this comes up I assume people have actually never done cosplay or haven't spent much time around cosplayers.
Cosplayers spend 50% of conventions fixing their outfit. It never lasts the day. You can't be tinkering with outfits on an 8-12hr shoot day every single time the person takes too big of a step or walks up a flight of stairs.
The woman on the right in this image is standing completely still in a "normal" pose for a still photo. Go have her do 6 days on a film set and let's see how that outfit turns out.