This is likely a bad deal for the German taxpayer and a great deal for the corporate landlords.
Essentially, the Berlin gov has given the corporate landlords a profitable exit for their investments. The corp landlords, seeing the writing on the wall and fearing lower rents, unrest among tenants, and diminishing exit opportunities via selling to the market (which wont want to deal with the risks) can now exit by selling to the government. The German / Berlin gov gets an investment that is all but guaranteed to be a loss assuming they drop the rents for the tenants. Thus, tax payer eats the loss.
I see something similar playing out in the US, and not just for corp landlords - it could happen to baby boomers looking to sell their homes upon retirement. During the last housing crisis in '08, Alan Greenspan and Warren Buffet suggested buying homes and destroying them, effectively lowering the housing supply in order keep prices at the same level in a market with lower demand [1].
Key takeaway from all this - governments and the folks that influence them (who also own and get their primary income from assets) wont let asset prices go down. They would rather destroy assets and lower supply to protect price levels. This dynamic teed-up a political war between those who own assets vs those who do not, young vs old, establishment vs anti-establishment, etc.
I feel for tenants - I am one myself. However, better to let the market to clear market inefficiencies.
[1] https://www.fool.com/investing/general/2011/10/06/creative-d...