On the contrary, quite a few similar organizations do exist, but only when a government monopoly doesn't kill competition in that space. For example, who in the 90s would have guessed that something like TrustE would exist. It's not that far fetched to imagine that if government wasn't policing restaurants a private organization could exist to provide such a service. Yelp doesn't do that because it's not their mission and no one is going to make that their mission since the government already monopolized that job.
I'm not saying we should have 0 government either, but if we're not willing to question the necessity of things as trivial as local government health inspectors then where do we draw the line?