why do answered questions get deleted?

I've noticed that some questions get deleted after being answered. I assume the OP thinks nobody else would benefit from the solution. Or, are there other explanations?

Answer 1

[Zakary Stone]

The people who asked the questions may have deleted the questions themselves.

[bym]

yes, I know that, but why?

[Walter Roberson]

Unknown. I know that just a couple of days ago I had to use the google cache to dig up a copy of an answer that I had given someone, because the answer was relevant to someone else. It would have been better if the question had been left.

I do know that the Mathworks team believes that messages should preferably only be deleted in unusual circumstances, or if they are spam or obvious duplications. Mathworks is not the one deleting the questions.

[bym]

I did not want to imply that TMW was censoring answers beyond the spam. Perhaps the OP feels embarrassed, or perhaps more cynically: the OP does not want the thread to be obvious for ethical reasons.