So, in case of those countries you can say that "landlordism is a significant part of the country's housing sector".
It's the same story throughout much of the Americas, certainly all across Western Europe, and likely most of Eastern Europe as well. There are many contributing factors (this is by no means an exhaustive list):
population (since 1950, world population has more than tripled; US and Europe population has more than doubled)
globalist megacorporations and billionaires hoarding wealth and property generally
corporate landlords hoarding housing properties specifically
shrinking of the middle class, reduced purchasing power of the average citizen, etc.
bullshit jobbers, predatory investors, "free market" capitalism but with golden parachutes and tax breaks/taxpayer subsidies for the "haves," etc.
China et al. buying up properties and companies in the West
fewer government policies supportive of/conducive to nuclear family units, home ownership, etc.
Good luck and God bless, because we're all going to need it in the coming decades.