A good approach Skisy, the standard dictionary answer is a perfectly valid one. It makes 'why; relate to something that is going on or that is being considered. Why don't I give you a lift depends on the person being questioned making a journey. Why relates to How? Who? What? Where? & When? It implies motive, where somethings may just occur - The Universe exists because a god or gods had some motive to create it or it simply is, with there being no reason why other than the ones we subjectively assign to it's existence.
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