Human behavior. If you've got a population and you tell them to do X or they'll be labeled a criminal, you'll still have huge swaths of people who won't do X be

Human behavior. If you've got a population and you tell them to do X or they'll be labeled a criminal, you'll still have huge swaths of people who won't do X because of laziness, apathy, and/or ignorance. That's why opt-in vs. opt-out makes a such a big difference. Making this opt-in by default makes it extremely easy to target those who opt-out (and make judgements based on that action), but impossible to say anything remotely accurate about those who took no action.