It is all the other costs. A single person pays more for accommodation than a couple. They still have to eat, but smaller portions are more expensive and takeout is probably more common. They will likely have a car but just for them etc. In a half lifetime, it likely adds up. I wonder how much of the housing crisis that some countries are seeing would be eased if there was more cohabitation?

It is only one factor in all of this, but I think that incentives for business is aligned where they will make more money from people isolated than together. Even the Time on Site (ToS) metric is more geared to isolation. When was the last time you sat down with your family and read the online news?

So much of the consumer world today is for individual enjoyment more than shared experience. Even watching Netflix with my wife is more individual than it should be, and after talking to others, people are still checking their phones whilst watching a movie with others.