They have tried this approach. Keeping the existing buildings in use - or rather re-using them - consumes too much effort. The tiny houses coming from Sweden do not require maintenance - and shall easily be replaced when showing deficiencies.If 90% of the Netherlands has died from the plague, and all the existing houses are not destroyed and empty, why do people live in small wooden shacks ?
Amd why does Germany not annex the country outright ? If the climate gets colder the eastern areas of Germany will lose productivity while the Netherlands will stay milder close to the North Sea.
And control of the Rhine estuary and the Rotterdam port and railways and roads to the East woud help Germany enormously, shorter shipping routes.
The Germans have lost 10 million people in the pest. Not even the DVP hardliners claim that more Lebensraum is required.
The Rhine estuary is again the swamp it used to be before the Dutch started amelioration. Rotterdam has been abandoned. The Germans use the channels to shuttle their goods from Rhine and Ruhr to Bremen and Hamburg.