(nods)

I generally assume that people will understand "Why did you X?" to mean "You should not have Xed"... as a challenge, rather than a request for information, since such challenges are frequently expressed as questions of that sort. So if I genuinely want to invite people to reflect on their reasons, I find I have to reframe the question.

Depending on the particulars, that might be "When did you first decide to X?" or "What was your inspiration for X?" or even (though this is a dangerous one, as it skirts the edges of challenge) "What led you to reject Y in favor of X?"