Earlier quoted context omitted.
Demand can be affected by people living together, or encouraging that in some way. Be it having roommates, elderly parents living in, staying with ones parents longer, communes. None of them popular long term I think. Hence: supply
But not the rich, right? The rich don’t need to cram more people in, everyone else does. True?
Some may argue that the rich help in the supply by building new houses, but that makes them even richer. If it doesn't, they don't bother (a point from this article).