Dunno really. Some people may think that asking "why" implies a lack of belief or acceptance of their assertion, and is therefore a personal insult of some sort. Truth, sometimes folks are right in that interpretation....I know a least some of the time my "why"s imply that I don't believe someone YET...frequently because I simply don't understand them. I don't think their dislike implies they don't have an answer or haven't thought deeper (although sometimes they haven't), I think it's just that they think it implies a lack of respect. At least, that's what you'll get with some of my family.

Still, I think any Why question, however motivated, is good...it can't help but make a shallow conversation deeper. Lets you talk about reasons instead of just comparing conclusions.