It would have never occurred to me either; I always cook pasta al dente and love it that way. But while researching for this copycat recipe, I found that most people instruct you to cook the noodles for that long. The long cooking time ensures that the macaroni absorbs as much water as possible from the very beginning before being mixed with the cheese sauce. That again ensures that they won’t absorb too much of the cream and milk contained in the sauce. This way, the dish is as creamy as it can possibly be.