Why is asking "How?" expensive?

If you attended the typical American public schools, you probably first learned that questions begin with one of the five interrogatives -- Who, What, When, Where, and that immortal troublemaker, Why -- and only much later, possibly even after a good night's sleep, learned that there's actually a sixth; naturally, the canine charicature rarely ever opens with any different question, and its wild sibling rarely pauses howling to even make the question any more specific. Is there any readily articulable reason for the first five interrogatives being so preferred by human civilisation, while the sixth remains the subject of jokes? // [NO;]