I have to agree here. The "Why did you do it that way?" question alone is very irritating. But, when the question is followed by someone's idea of faster / smarter / better, it provides insight to a solution that may be more than the original intent.

I've had people answer some of my questions with little more than the "Why do you want to do that?", and I realized that they have their own way of thinking, but didn't want to share it. And simply saying, "Don't use that, use this instead", without giving an example of usage is little more than taking a tool away, and replacing it with a different tool that the person hasn't a clue how to use. They still won't have a good answer, and they are likely to be more confused than when they started.