The Baby-Boomer generation in the US is increasingly deciding to "age in place" rather than downsize and/or move to assisted living facilities. This is certainly a factor in the ownership figure you are quoting. There has been lots of coverage in this trend the last few years as well. See:

https://www.nytimes.com/2021/07/08/realestate/baby-boomers-r...

and

https://archive.ph/0LXQu