Taxis, for all of their warts, have a number you can call, someone in the local government you can contact, etc.

How is Uber or whatever that different? You can call the police, which are already someones "in the local government you can contact".

And neither the police nor a taxi commission are capable of doing much to protect anyone before a crime is committed (except by the usual channels, e.g. credibly committing to punishing criminals).

Yes, you can contact someone who won't give a crap. That's what you get for paying the monopoly price for taxi services.