What is the purpose of only notifying 65% of the sites found (and publicizing it that way)? Is that to create some uncertainty, so that even sites that weren't

What is the purpose of only notifying 65% of the sites found (and publicizing it that way)? Is that to create some uncertainty, so that even sites that weren't discovered by this method will give some thought to changing, for fear that they are part of the 35% not notified?