HTTP/2 gives you more than just a stream of frames (matching of requests to responses, some structure around headers and bodies, flow control, etc). gRPC could

HTTP/2 gives you more than just a stream of frames (matching of requests to responses, some structure around headers and bodies, flow control, etc). gRPC could have been built on websockets but it would have been more work (almost as much work as building on plain TCP sockets - websockets add very little except the ability to work from a browser)