Does the Maps Destinations widget which shows this information still appear on your iPhone? I had the same problem with my Watch, and was frustrated by it. But it had also stopped appearing in the Maps Destinations widget on my iPhone, so there was no way it would appear on my Watch.
What I ended up doing was going into Settings, General, Reset on my iPhone, and resetting Location & Privacy.
This fixed the problem for me, and I now see the destination estimations (traffic is light, traffic is heavy, take xxx route, etc. etc.) on both my iPhone and in the Siri face on my Watch.
NOTE: After doing the reset, whenever you start an app that uses location/privacy for the first time, you'll have to grant that app permission again. I'm not sure if there's another way to fix this issue, but the above certainly worked for me.