I think for a why question to be a good one, it must reach some point of education that isn't just for knowledge of programming/computer trivia, but is useful information to know for programmers.
A good example is:
Why Is Processing a Sorted Array Faster Than an Unsorted Array?Why Is Processing a Sorted Array Faster Than an Unsorted Array?
This question asks about a programming issue that is very relevant to most programming, and it has great answers that really go into the nitty-gritty details.
Another post that educates on a subtle point in programming:
Why Does Python Code Run Faster In a Function?Why Does Python Code Run Faster In a Function?
