Because posting asking why something got deleted is not terribly constructive to the mission of HN. It just adds noise. If you have issues with the way the site is run, making drama on the frontpage is not a great way to settle things.
I don't think anyone had issues; they were just confused and asking for clarification. If it's not constructive to have such things on the homepage, then let it get buried by better subjects. Deleting requests for information is just going to engender more confusion, and thus score more upvotes for the next request for information. Case in point: this thread. Which is currently on the homepage.