What do people mean when they ask "why"?

I feel like many people often approach a question asking “why” by answering “how.” This works for smaller questions with practical implications like “Why should I read the boilerplate provisions in a contract,” but doesn’t work for the larger questions. There, the separation between “Why this happens” and “How this happens” become more distinct and I believe should be recognized.

Unfortunately…I often see people answering larger “Why” questions with “How” answers, and trying to argue their point. This can only create frustration, however, as the answer to “Why do we have thought?” answered with something involving the electrochemical impulses and brain structure begs the question “Why is the brain structured that way?” When the how person answers with an evolutionary explanation, the “Why” of HOW that happened is the follow up. This can continue ad infinitum.

So, if you know that someone is asking “Why,” why do you continue to answer how?