Everyone feels a special need to fill in moments of silence with small talk whenever they are around other people. People unconsciously fill in those moments with bullshit sentences that don't mean anything at all. It just feels really awkward when no one is talking. That doesn't mean that there always needs to be something to talk about; there doesn't. It just means that there can never be nothing to talk about.
And those moments where nothing comes to mind? Hm... Never thought about that.