Thanks for the response, and sorry for taking so long to react. The ‘why’ question is perfectly legitimate, but it tempts us into the shortcut of answering with personality, rather than circumstance as an explanation. By asking the ‘what’ question, we’re less likely to do that (because of course we are a ‘good’ person), and seek out contextual explanations.
I do like your “coarse extrapolation”! Asking the ‘why’ question about things that happen to you can quickly lead to the supernatural. There is often no sensible answer to the why-question around (negative) life events. “What did I do to deserve (to lose my job three times in a row, have my house burn down, my wallet stolen etc.)?” — doesn’t really lead to anything meaningful. Using ‘what’ instead is indeed likely to lead to more objective explanations, and indeed to more happiness. Excellent point!