I just found this out as well...
The HE google home integration doesn't support motion sensors or contact sensors.
https://docs.hubitat.com/index.php?title=Google_Home
However, there is a Community Provided Google Home Integration that does:
If you would like to use "unsupported" devices, the community integration supports a wider range of devices: [Alpha] Community-maintained Google Home integration
The implementation of the Hubitat Google Home integration setup is confusing and doesn't make it clear enough that such common devices like motion and contact sensore aren't supported. Hopefully they will fix that in a future release.
Thread here where I asked that same question just a few days ago...
