Nice find.
This is because docker-machine will tend to use the DockerNAT switch by default. I tried creating a separate external switch and using that, as mentioned in the docs. This works fine:
docker-machine create -d hyperv --hyperv-virtual-switch external-switch tempbox1
Overall, we don’t envision users using docker-machine to create more local machines (it’s included to create remote machines).
I’ve created an issue to track documenting this more clearly.