I think the building restrictions parent poster was referring to are density restrictions.

As an example, there are narrow strips of Toronto along major roads that allow skyscrapers, a lot of it a block away from single-family-home zoning. So all the demand for multi-unit housing bursts up in narrow corridors.

If, instead, quad-plexes became universally allowed, and lot height limits were increased to 3 (or 4? idk) stories, then single-family homes could be torn down or renovated to make room for up to 4 families to live comfortably on the same land.

Rosedale shouldn't exist. Single-family homes a short walk from downtown Toronto is a big part of why people are commuting from Barrie.

West Van is just as bad. Even small towns in desirable areas are seeing density restrictions causing a missing middle in housing.