This effects new sites. For existing sites that have it set to false it will remain false. We often find wonderful sites that judging by the content are clearly meant to be public but the site’s owner hasn’t clicked the “public listing okay” so we can’t share them with you all. I’m pretty sure in 99% of these case the site owner just didn’t get around to visiting the control panel and ticking that box it, so that’s the reasoning behind this change.