I feel the word "why" asks for an answer that gives a reason or a purpose.
Is that appropriate for a Q&A about Earth Science?
If you look at the questions on the physics SE site, I believe the occurrence of the word "why" in Question/Titles is much less frequent than here. This may be because questions are edited to encourage asking "how" or "what" or "where", rather than "why" something is the way it is.
Discouraging the over-use of the "Why" may improve the Q&A on the site by helping the questions to be more focused and encourage expert participants to answer.
I don't think a ban on the use of Why in questions is desirable. But I am thinking its overuse is a symptom of insufficient thought and research prior to writing the question. So maybe its more of a flag for a question that is in need of improvement.
For example, a particularly frustrating example was: "Why does the Earth rotate counter-clockwise?" There is just too little information there to know what is being asked, and perhaps the person asking would have come closer to their target had they been asked to rewrite it without the why. This could be done in a comment, but it should be done in a way that does not lead the questioner.