It's an important information-seeking question!
But, for some reason, in many geographies, here, in the US, people often (apparently) take it to mean something like "I don't agree." or "Justify that.". And that triggers defensiveness, and then you aren't getting information.
Because my goal is the information nugget at the end of the quest, I've learned, with most people, until I know them well, to use something like these instead of "why?":
- "Interesting. Why did you decide to do it that way?", or
- "Really? How did you prioritize the trade-offs to come to that conclusion?"
I don't know if that makes Americans thin-skinned, or just sensitive to that one word, or ... what ... but I think that most Americans most of the time would prefer to not offend, and have learned that challenging another person's opinion is viewed by many to be offensive. It's highly inefficient, doesn't work well in multi-lingual meeting settings, so I'd guess the Americans you have been exposed to are are somewhat experienced in international business?