If there are 1000 units and they are being rented out then people are more willing to move to a residence that suits their needs better. When it makes sense people move away.
Once you add rent control people might stay simply because of the low rent, even if they are fully capable of paying market rate rent. They might have to commute to the edge of town and it still is a better deal for them. You get a stagnant housing market where people rarely move. The vacancy rate goes down and instead of renters always being able to at least visit an apartment with the fair chance of competing with say 5 people at most you now have dozens of renters all looking at the same apartment. This gives the land lord more power to charge higher prices and since he has to cancel out the losses from existing rent controlled apartments he might not even have a choice and simply increases the rates when possible.
The problem is that the land lord is being put under more pressure to perform and thus he becomes more selective and only gets the "best" tenants which favors the wealthy.
Of course, all those people getting paying dirt cheap rent are happy since they benefit personally from an externality.
Once you add rent control people might stay simply because of the low rent, even if they are fully capable of paying market rate rent. They might have to commute to the edge of town and it still is a better deal for them. You get a stagnant housing market where people rarely move. The vacancy rate goes down and instead of renters always being able to at least visit an apartment with the fair chance of competing with say 5 people at most you now have dozens of renters all looking at the same apartment. This gives the land lord more power to charge higher prices and since he has to cancel out the losses from existing rent controlled apartments he might not even have a choice and simply increases the rates when possible.
The problem is that the land lord is being put under more pressure to perform and thus he becomes more selective and only gets the "best" tenants which favors the wealthy.
Of course, all those people getting paying dirt cheap rent are happy since they benefit personally from an externality.