People often say no problem if landlords sell because the homes are still there. True, though many owner occupied places have fewer occupants than rentals, and some rentals are converted to other uses. But a key problem is that the rental pool is not keeping up with demand including net immigration. New bank lending for residential lending is way less now than say 3 years ago, to the tune of thousands fewer rentals each month.
You can say landlords chuck their toys but actually they are doing very well through higher rents paying for the required upgrades and compliance, better returns from short term rentals and big smiles as they bank their tax free gains.