It's like how starting to tear down you Artist Alley table triggers a sudden surge of customers: deciding to head back to your room and change costume causes more people to want to take your picture, doubly so if it's an obscure/weird costume that nobody was getting in the first place.
And the staffer lady even said she was relieved I actually DID turn out to be a Gravity Falls cosplayer and not just a dude with a really fuzzy hat.