It's not necessarily about gossip and judgment. Consider two different kinds of friendship groups. There are small, close-knit ones, where everyone is friends with everyone, and everyone wants Alice to be there. And there are large, loose ones, where if Alice doesn't show up, nobody might even notice.
In the first case, if Alice isn't on facebook, they might make plans on facebook and someone will say "cool, I'll let Alice know". In the second case, they might make plans on facebook and nobody will think to do that. Her closer friends might - but her closer friends might not even be going, and that doesn't mean she doesn't want to go.
In the first case, if Alice isn't on facebook, they might make plans on facebook and someone will say "cool, I'll let Alice know". In the second case, they might make plans on facebook and nobody will think to do that. Her closer friends might - but her closer friends might not even be going, and that doesn't mean she doesn't want to go.