My guess is they set a goal for you to encourage you to speed run. Once you A+ it, you feel more comfortable trying to shave off time. If there wasn't a goal time set, then you may feel too overwhelmed to challenge leader-board times, thus never reentering after completion.
GameFAQs, where there's an opinion... there's a fight. Never argue with an idiot. They drag you down to their level then beat you with experience.