Nature deplores a vacuum, and silence will draw someone out. Counter-intuitively, it also gives permission for people to speak who otherwise would be too shy.
I'm wondering if that has to do with internal "speed"/timing issues. My ex was a slow talking, quiet sort (and shy/introverted) and I tend to talk a lot and talk fast. A big issue in our marriage was when we argued and I felt like I took really huge pauses to try to get him to speak but he still wouldn't speak so I would resume talking to fill the silence. His take on it was that I never ever shut up and there was no way to get a word in edgewise. I imagine if we had overcome this issue, the marriage would have gone a great deal more smoothly. I had to actively teach our younger son, who is more like his father in this regard, to simply "interrupt" me and his fast-talking older brother. Otherwise, he feels like we don't "let" him talk. There is a big disconnect in the internal timing here -- he seems to not be able to judge how/when to jump in the way his brother and I do. So when he simply "interrupts" us, I defend it if his brother gets irritated or something.
However, a separate but related trait is that I often find myself internally running through several iterations of what I want to say, only to realize that by the time I've winnowed it down to the relevant info and am ready to speak, the conversation has moved on.