I'm literally one of those people who you say is vanishingly small.
It's not even a "the world is bad and I don't want to subject my child to that" kind of decision. It's more like a series of thoughts over the years: "is this the right time to have a kid?" and it's never a good time.
Even more interesting is how all of Geelong is excluded from Melbourne's count when Gosford's included in Sydney's count, despite neither place being continuously connected to the larger city, Geelong being closer to Melbourne than Gosford is to Sydney, and Geelong having just as large a proportion of daily commuters as Gosford.
The reality is that Melbourne's population outpaced Sydney a long time ago and the boundaries are only just starting to catch up.