SMS would argue that the incentive to doing it the old-fashioned way and going up from karts to Formula A is the career goals achievement they've built...but honestly, achievements never meant a thing to me. A game giving me a pat on the back for accomplishing something does literally nothing to my motivation.
Then again what you're describing is kind of the way Toca used to be, and that was awful cause you had to win like eight disciplines before you could get into an F1 car, and there are few things more boring to me than having to endure a full season of Formula Ford or Formula 3