Agreed, there are hidden teachers you may come across in life that conceal their understanding from the world at large (i.e. remain silent until the student appears).
On the other hand, there are awakened beings like J. Krishnamurti who prattle on endlessly (eloquently so, mind you) about the no-path to awakening.
Also, in the Zen tradition it's pretty common for the master to give Dharma talks, which of course entails lots of talking (Eihei Dogen comes to mind here, saying a lot and revealing little for the rational mind to latch onto).
Probably the best example of "Those who know don't say" in recent times was Ramana Maharshi.
The introverts, they are the ones that go within and cut themselves off from the world. They are the ones getting "enlightened".
The extroverts, talking all the time and sounding important, barely know what is what.
These are two remarkably different ways of coping with the same problem: fear.
Seriously, the introverts need to find a way to talk, and the extroverts need to calm down and feel more.