Uh, don't you get the 2 million signing bonus after you were scouted and determined to have useful skills?
Kind of, but it still doesn't make you a top prospect. The bonus is to dissuade you from not signing. In baseball, players that are drafted can return to school if they don't sign with the team. Or they can go play Indy ball.
Like any draft pick, you have some sort of skillset that the scouts think can be projected and developed. But simply being given a signing bonus doesn't automatically bequeath you "top prospect" status. Like I said, Bubba Starling got 7 million and right now, the Royals would be lucky if he turned into Brian Goodwin.