Or, they didn’t sell it and are just seeking rent on it, now. For this effect to really work, the number of home-owners should equal the number of homes.
Right now, there are many, many fewer home-owners than homes.
That's fine, it still provides housing for someone. And there are people who actually prefer to rent, so it's good to have rental units available.
Problematic is when they hold on to it and keep it empty, thus occupying space but providing housing for no one.
(Slightly higher because it is mathematically impossible for anyone to move if there are no empty homes, and they sometimes have to sit vacant while being renovated or are in the process of being sold)