Voluntary food safety postings are useless, because they allow fraudulent posting. Sure, it'll come out pretty soon - but by that time people are ill or dead due to food poisoning, and the person in question is likely long gone.
"The market" doesn't give a shit if actors are fraudulent or working with good intentions, and it has no way to prevent turning an iterated situation into a one-off situation. "The market" has no idea which reviews are genuine. If you'd like to see unregulated reviews in action, look at the direction yelp is turning lately. "The market" does not guarantee that consumers are fully (or even somewhat) informed, a condition that is necessary to a market actually working properly.
> Or it would be a competitive advantage if the markets truly benefited from food safety scores for newer restaurants to advertise them where their entrenched competition does no such thing.
No, it wouldn't, because you'd have no idea if you could trust the reviews. So you'd wait a while. Sooner or later, you have a bunch of restaurants that post reviews. And then new restaurants pop up, also posting their reviews. Do you still know which ones are trustworthy and which ones aren't?
Sure, you could ask your friends. Until you travel. At which point you're at the mercy of complete strangers.
"The market" is not an almighty force for good. It allows efficient exchange of goods. If a cost is externalized - say, the hospital bill of people eating at restaurants - the market does exactly nothing about it. Because the cost is externalized.
That's the whole point of regulations. Not to be a pain in the neck, but to ensure costs are not externalized. The only way to achieve that without enforcement is a society of entirely benevolent actors. That does not exist.
