@Johnnypenso -- There are always multiple ways of doing things, though. In any game where you can adjust the AI difficulty, there's nothing stopping you from playing on "Medium" to complete events and/or unlock things, then switching it to "Very Hard" to battle the AI, after you've bought and built up your dream car with the money you earned. It's no different from adjusting the AI % in PCARS in accordance to your skill level -- anyone can play to win, or play for the fun of battling the AI, or both.
I suppose Gran Turismo doesn't allow you to change the AI difficulty, so there's your problem. It's no reason to discredit the idea of a game economy entirely, across all games. Some people want more than just simulated racing. We also like to play videogames. Currency and winnings are elements of game design.
Before anyone gets the wrong idea, I'm not asking for an economy in PCARS. A career mode that tracks your progress and provides structure and permanence to your race results and achievements is another approach to game design, and one I look forward to trying myself.