The "household size" in that article is trending down, which suggests that, if more young adults are living with their parents, it's counterbalanced by more people in other age groups living alone?
There has been a decline in households with four or more people and a rise in households with one to three people, but our housing stock tends to be geared towards nuclear families with a breadwinner father, homemaker mother and 2.5 children.
Last I checked, average new homes post-2000 were more than twice the size of new homes in the 1950s and held one less person on average. So you are seeing couples with one child buy four bedroom homes and turn the extra bedrooms into an office and a playroom or hobby space.
Meanwhile, the poorest of the poor are often unable to find housing at all. We have a lot of homeless people.
This would be much less of an issue if there were more affordable units. It's extremely hard to find units below $500 in the US. If you could readily find units for $400-$600, many people who currently can't afford housing would be fine.
I’ve moved on to trying to buy an RV park or campground, or build one, and use tiny homes or Boxable for the structures. The purpose of a system is what it does, and it is not to get people into affordable housing. It is to protect property values and NIMBYs' desires, with a second order effect of disincentivizing density (even slight increases of it). Deeply disappointing for someone who works with the unhoused and is just trying to get them into housing that isn't a shelter or a tent behind the park.
It's the price itself that is the issue.
Don’t put the onus on the private sector. You want landlords to make it easier for people to rent? Either have the government have programs to guarantee rent or make it easier to evict people for non payment.
There's likely other factors.