Since it’s currently April, these ways are considered closed to all types of traffic according to the current tagging. If this isn’t correct and the road isn’t always closed for the months of December to April, then the tagging will need to be fixed.
All right, I wasn’t aware of the existence of that flag and I did not discover that flag in the editor either. I’ll have to look again.
However, I now want to plan a journey that I want to undertake in June, and by then the road will be open. Is there a way to force routing?
I would prefer a behaviour where the routing over that pass will be performed and, perhaps, the restricted area of the trip should be painted in red, and upon hovering a popup should appear telling me that road might be closed in winter.
The OSM web site gives access to several sample routers. There will be others. I think all of them are maintained by third parties, but without knowing which router you are using, it is difficult to direct you to the correct place for making features requests.