On the flip side, I don't need to know who you voted for--or who you retroactively voted for now that you know the result. It's generally virtue signaling or prompting (I showed you mine, now you show me yours), though for ancient history it could be just background. Maybe you think you know what my motives are in picking one Senator over another. AVI would say that I probably only have a fuzzy picture of that myself, and that a lot of our reasoning is ex post facto rationalization.
I have, in the past, explained why I deprecated one candidate or another. (That's shooting fish in a barrel this election--and everybody else has done it already.) I doubt that I persuaded anybody, but I tried, and persuasion is part of the game. But still, don't ask. The man with the 6' Trump sign probably didn't vote for Jill Stein. Don't ask. (Do you floss every day? Don't ask. Boxers or briefs? Please don't ask.)
This year's presidential election I think shows even more clearly the value of this little courtesy.