Have you even wondered why this "game-saving" thing was not included in the initial release of the game? And also why cars have corresponding price and levels? Its because if you want those cars, you need to earn the credits and gain the exp points for you to be able to get it. Its basically one of the objectives of this game.
But there are some complaints that some systems are crashing and are losing their saved game data. So to help these people solved the problem, they unlock this "game-saving" thing. But the problem with some people is that they exploited this thing. They were given a hand but they took the whole arm. In the process, all the values of the prized-cars were gone. Why earn the credits if someone can simply dupe it for you? So some of the games objectives are now irrelevant. In this world, everything has a price. you give some, you win some. You give hard effort, a reward is waiting for you.
So tell me, was the game not ruined? If for you its not, then you should have stayed in the arcade mode. Because obviously that is where you belong..