Maybe it's something else I'm missing, which is why it would be good for Moxie or Whatsapp to clear up this puzzling choice.
Also I hope both the Whatsapp and Signal teams think of ways to encourage security code authentication through better UI. Viber, for instance, has taken an interesting approach to encouraging easier authentication. It probably still doesn't go far enough to make it easy enough for just about anyone to want to authenticate their contacts, but I'd like to see more of this sort of UI experimentation:
https://support.viber.com/customer/portal/articles/2017401-v...