Why are closed roads not shown on maps and if no reasonable alternatives are given?

EisbärNC700 Registered Users Posts: 1
Apprentice Seeker
I have been travelling last week of August with my bike in the German Bundesländer Sachsen and Thüringen, where I have been confronted with several closed roads due to intensive roadwork (they must have started some time ago and/or still will go on some time).
But in most cases, these were not shown on the maps nor my TomTom550 gave alternative options to bypass the closed road. In one case it indicated to me to return about 20 km back where I came from. That is not acceptable. What could be the reason for these missing closed roads updates? And how to get better and shorter options if a detour is necessary?