Google simply returns human written results, so delegating the trust problem. You can track author's record and judge if they're trustworthy yourself. Doing the same thing for GPT-3 is much harder. How are you going to debug the model? Probably there is only a handful amount of people who is capable of debugging the model even with all necessary access granted. You can think it as autonomous driving which already has reached to a good level for 99% of use cases (at least for Waymo and Cruise), but no one think it's going to mass deploy robotaxi anytime soon.