Housing shortages can suddenly disappear in the absence of new housing. These shortages were likely a result of artificially low prices for accommodation imposed by the government. While landlords can’t charge as much as the market would bear, citizens who are otherwise disinterested rent the apartments because it is cheap.
In such a scenario, the removal of rent controls would motivate residents who do not value the property at their natural value to vacate. Those willing to pay the prices will now be able to find housing. Downsizing will occur in those who occupy more space than they need, and now larger families can move into the bigger apartments after people downsize.