If you look latino, and live near the Mexican border - the odds would be lot higher than that.
My neighbor is a naturalised citizen, is latino by appearance, and has heavily accented English. We live in Southern California. He carries a passport card in his wallet. The other night he was pulled over in a traffic stop - reason for the stop is unclear, but, it was late, he was in his beat-up work truck, in a fairly isolated area. The police officer approached the car with his gun drawn, and my neighbour was called out of the care, and had to lay on the ground. He told me the police officer asked him if he was illegal, and threatened to arrest him. He was able to show his passport card, prove citizenship, and drive away. If he did not have the card, he may have been detained, had to call his wife and have her drive with citizenship certificate etc.
So, whether you want to debate the legality of having to be able to prove citizenship, in some circumstances, it just seems good common sense to carry it with you.
On the other hand, I am a middle aged blond caucasian female, and drive a boring newish crossover SUV - I may love in the same area, but feel no need to have a passport card we me.