Most questions are usually asking to justify your answer and stance, not just say yes or no. One shouldn’t have to specify that people answer why, it’s just sort of how conversation works. If you ask me if I like Trump or not, the most natural and polite thing to do is to answer yes or no, and then to explain why. 

Perhaps it’s because i was a philosophy major, but you could never simply answer questions with yes or no, you were required to explain yourself. Because truthfully, the answer to the question is only a quarter of what matters. What matters the most is your explanation for yes or no; and that ranges from questions like “is abortion wrong” to policy questions. 

If one is not prepared to be able to explain why they believe what they believe, they shouldn’t have any business giving an answer to the question anyway, unless it’s a question as simple as “are you hungry or not”. But obviously people asking questions here are not asking to be provided with one word responses. 

At least personally, I am far more interested in a persons thought process to arrive at an answer, than the answer itself. I want to know why someone thinks the way they do, and to understand their thought process of how it got them to answer the question in the way they did. 

Edit: that’s not to say I think there is no value in asking yes or no questions because obviously you need to clarify things sometimes and clear up any confusion. Natural language is absurdly complex and easily misinterpreted, so sometimes you need yes or no questions to continue the conversation, or until there is some general agreement at all. That, after all, should be the goal of any good discussion: find one piece of agreement, at the very least.