What's interesting about the replies to this comment how readily people provide post-hoc justifications for language features that often have no essential rhyme or reason. The same is true for the prepositions which accompany verbs, which tend to vary by language, but for which every language's speaker will gladly offer you "rules" or "explanations" for when they fit. It's great evidence that we can be very good at something with no communicable understanding of what it is we actually know.

Usually happens when a person answers a "why" question to something they did without thinking.