Answer enough How questions and you get to a lot of Why questions.
Disease, birth defects, storms, drought, earthquakes, floods, meteorites, etc. All of these have at one time been Why questions, and are now How questions.
"All of these have at one time been Why questions, and are now How questions."
Yet "Why" remains unanswered. What benefit does it serve for us to have disease, if disease is in fact only here to kill and make things live a painful life? We can know "How" from any number of positions, but we still can't come up with a scientific REASON for it. Only an explanation of it's mechanics.