Grpc http2Server: Why context.Background()?

Why is the server request context not derived from a user provided context?
Instead, it’s privately created as context.Background() here:
…/go/pkg/mod/google.golang.org/grpc@v1.27.0/internal/transport/http2_server.go:219

	t := &http2Server{
		ctx:               context.Background(),
		done:              done,
		conn:              conn,
		remoteAddr:        conn.RemoteAddr()
         ...