Why is it that googling “living density” or “liveable density” yields no search results?

I refer to the HDB’s reply “13,700 people per sq km is living density, not population density” (Straits Times Forum, Apr 24) to Mr Cheang Peng Wah’s  letter in ST Forum  (20 Apr).

It states that “Housing Board chief executive Cheong Koon Hean’s lecture was about how Singapore can anticipate its urban future and develop “liveable density”. The figures cited were, hence, on living density, and not population density.

Living density takes into account only the land available for urban areas, and excludes land used for ports, airports, defence and utilities, among others. It would be inaccurate to extrapolate the population size from the living density figure.”

I googled “liveable density” or “living density” and could not find it in the search results?

I searched “liveable density” or “living density” in thesaurus.com and dictionary.com and also could not find it in the search results?

In contrast, “population density” can be found easily in all the above three portals?

I could find “liveable density”, but only with reference to Singapore?

Leong Sze Hian