What's your justification? There's nothing wrong with the game.
I also see nothing wrong with the game.
Agree with the decision or not, the game's rules explicitly, to my understanding, allow a contestant to walk out at any time with the sum of whatever cash values appear on the die faces. Even if there is just one die face with cash showing and it happens to be $500 ... the contestant can walk away and keep the cash.
Now, maybe this will be the spark that pushes the producers to offer better cars, or maybe it won't. That's up to them. Then again, even if in theory a fully-equipped, top-of-the-line Cadillac XTS (nee DeVille) were offered we might see some people walk -- although I'd suspect that would be for a prime-time special and the cash values increased, but that's a completely different story.
Anyway, who knows if "better cars" would give future contestants more an incentive to play on, or ... as this case apparently is ... this was a contestant who -- regardless of what model of car was offered -- was satisfied with his winnings so far and made a perfectly allowable decision to quit and we just have to accept it.
Again, do I support his decision, even if I disagree? Yes ... because it was the right decision for him.
Brian