The trouble is, the advertisers want exactly those users who would be willing to pay money; they're high-value eyeballs. By allowing their most valuable users t

The trouble is, the advertisers want exactly those users who would be willing to pay money; they're high-value eyeballs. By allowing their most valuable users to opt-out, they devalue themselves as an advertising venue. Of course, they also decrease the available impressions if a significant number of people opt out, making them a less attractive venue again.