Why is it we hear stories about Sensei who use silence to answer questions?

Stories or fables or folktales of Asian Sensei of history abound as the Stoic, hard, and uncommunicative person who gets up, preforms a technique maybe three times for the student, and then sits down and watches.

First, in Japanese groups such as martial practices the juniors or practitioners don't question Sensei. In addition, due to group-orientations of Japanese, they develop group specific rules to adhere to for group solidarity. This is through a development of "non-verbal communications, the distinction between uchi and soto, and the emphasis on harmony which is a part of the Japanese distinct group consciousness.

Japan is a society, major group here, which require a conciliatory, cooperative attitude. Both lack of speech and silence is seen as a means of communication. The Japanese have to become adept at perceiving these things in lieu of talking, etc. - mostly.

It is believed, mostly, that if a Japanese person expresses what they really think they could possibly "hurt the feelings" of others. It would also disrupt the group atmosphere thus resulting in the destruction of harmonious relations.

This is my terse answer to this question yet it is not complete due to the complexities of the Japanese beliefs, customs, etc. which means if you really want to understand all the stuff you use in the Dojo that is not American - research and study is in order.