I agree, but do we really need 300, 400 cars to make a good game? Not really.
If NFS concentrated on the amount of cars it had in its garage, then it wouldn't be as popular as it is today. It would be some sort of Gran Turismo arcade-style rip off. It wouldn't work. NFS has always been about the gameplay, and by focusing on that rather than the car list is what's going to get people to buy the game.
Well, you don't need hundreds of cars to make a game good but it doesn't hurt. What makes a good NFS game is a good story and the driving physics. Either way, I doubt EA could justify including hundreds of cars since it would cost so much money to obtain the right and profits would suffer.