Ask HN: Why my post get [flagged]?

There's only two ways to get flagged: automatically via defence mechanisms, or submitting something HN users deem inappropriate.

There already are moderators and mechanisms for HN users to "vouch" for flagged posts too, your post doesn't seem to be flagged now so I guess some people did that.

Your post reads as an advertisement.

That is most likely why the number necessary of users flagged it.

Flagging is from normal readers hitting the "flag" button (those with enough karma to obtain flagging rights).