Some of Google Cloud's critical APIs only seem to use gRPC over HTTPS. It relies on such an esoteric part of the TLS specification that many (most?) proxies can't carry the traffic. You end up hunting for 2 days to find out why your connections don't work only to realize they probably never will. So I would say it's good that gRPC isn't being pushed hard yet.

On a personal level, it's one of those projects that someone obsessed with "perfect engineering" develops, regardless of the human cost. Crappier solutions (ex. JSON-over-HTTP) are better in almost all cases.