I was involved in a project in a well-to-do community to convert 2 4-bed semis into a number of smaller apartments to provide properties for seniors to downsize and remain within the same locality. The project ran into a brick wall from the very start with opposition from all sides of the communityI happen to know quite a few seniors that are keen to downsize from large family homes to modern apartments. It can make a lot of economic sense.
The problem they typically run into is a lack of suitable apartments in their desired location.
So imho, the lack of suitable apartments is down to lack of understanding and foresight amongst political leaders who cannot, and will not, try to educate local communities on the benefits of having a mix of residences in a neighbourhood