Because the photographer said, "Smile for the little birdie!!!" and they still had a Twitter logo next to the camera instead of an X because they thought that meant the mugshot wouldn't end up on the 'net.
Maybe I should read the article..
Edit: oops, it's "defiance" I guess. Maybe we can get another mugshot after their sentencing to see if they're still smiling In defiance.
I guess that's because they don't want people to think they are in trouble. If you ignore the sheriff badge this could be a regular picture, and some voters probably can't tell the difference