i think there's an unconscious impulse to try to seem either servile or mysterious in conversations where you want to be liked or seem interesting. so it makes sense that people assume reticence to speak is a better tactic than talking a lot.
> seem 'interesting' without saying much is to elicit intrigue - or mystery, so you want to seem mysterious.
I'm sure there are people to whom that applies. But it doesn't seem likely to be widely applicable to me. Most people just aren't going for the "dark and mysterious" vibe.