While we concentrated new housing on a small percentage of our city's land mass, the protected Yellowbelt areas have been losing population. Where streets mostly filled up young families when the homes were new, many of those homes now have only one or two adults living in them, causing the aging neighbourhoods to lose population. School enrolment dwindles in these areas, while fewer people pay to ride transit in them, so some schools close and some bus routes have their service frequency cut back. While people liked to call these "stable" neighbourhoods, where we do not allow new housing, neighbourhoods do not actually stay the same: they hollow out. Meanwhile, where we concentrate new housing, those schools are bursting at the seams and the transit is overcrowded.

Pre-World War II, Toronto allowed duplexes, small apartment buildings, and more to be built side-by-side with single family homes. This meant the city's form was more dense, and more akin to even denser cities across Europe, which manage to easily house more people in the same area while still being immensely livable. Rapid post-war development in North America, however, came with stricter zoning, and and ended up creating a tale of two densities and extremes of housing that now dominate the cityscapes of Toronto and most of the continent's other biggest cities.

While single-family housing exploded in the suburbs, (creating a built form characterized by large lots and automobile dependency), until recently, high-rise condominiums and rental apartments fulfilled a demand for comparably inexpensive living within urban enclaves that support walking, cycling, and transit. Now those condos and rentals have also become unaffordable for many people, and the sweet spot provided by small multi-family buildings had become lost in the shuffle, leaving little room for the gentle density increases in hollowing-out neighbourhoods that could address much of the need.