Shadow banning (also called stealth banning, ghost banning or comment ghosting) is the act of blocking a user or their content from an online community such that it will not be readily apparent to the user that they have been banned.
By making a user's contributions invisible or less prominent to other members of the service, a hope may be that in the absence of reactions to their comments, the problematic or otherwise out of favor user will become bored or frustrated and leave the site.
They do it under the guise of directing articles and posts to "fit your interest". Basically, they don't want ignorant leftist to be exposed to real educational material, because who knows what might happen. They might #walkaway. The facebook jokers are doing it even when you post articles and comments that should show up on all your "friends" feeds.