Sorry, can't look up peer reviewed sources at the moment.. or copy paste for some reason. Its worth noting that the price controls are no more than 20% higher than local properties at the start of tenancy, and no more than 20% increase over 3 years. Still allows for roughly 40% increase Oliver three years and there are discussions on how landlords are taking advantage.

Guardian discussed how companies are discouraged from building in Germany and fuelled demand for existing stock.

Germany population is also in a slow decline (like, -0.xyz%) so new builds aren't as necessary as other places.