In that case: They should sell the units so other people can utilize it. In large parts of Scandinavia there is an obligation to have residents in an apartment

In that case: They should sell the units so other people can utilize it. In large parts of Scandinavia there is an obligation to have residents in an apartment. The only legal reason not to have an apartment occupied is that it is for sale, or on the market for finding a renter (within the market price). IMHO there is absolutely no reason to let units stay empty for any longer than what normal resident churn mandate.