No, because internal APIs for the same backends are more powerful and easier to integrate with. It's not easy to make the external APIs as useful and powerful as internal ones: for one, you can trust your users more to do the right thing and not try to exploit you for profit, it's much less committment to offer certain functionalities, since it's easier to roll them back if only users are internal, etc. Google is slowly getting there in feature parity, but so much effort has been invested in Google internal ecosystem even before GCP has even existed that, as good as GCP is, nobody wants to bet on it when obviously superior alternative is available.