The main bullet points I get for reasons involve

1. People work more. In particular, the shift to dual-income households means that women, who traditionally planned most parties before, no longer have time.

2. the shift to "lots of kids, sparse parenting" to "few kids, lots of investment" becomes another time sink focusing families inwards on themselves instead of outwards on the wider community

3. People just have less friends. especially so for a) single b) non college-degree and c) lower-income people. Probably due to #1 and the whole dating app epidemic no one has had a serious conversation about yet.

4. And yes, as you alluded to, it is "more fun to be alone" in the modern day. Less incentive to go out if you don't "feel" lonely nor bored.

I guess I could have just quoted the provided summary, but where's the fun in that?

>In sum: The death of the host is the story of lonely unmarried people and harried married dual-earner households; anxious parents spending more time with their children and less time with friends; and the typical home becoming such a riot of diverting comfort that people no longer have to invite human beings to interrupt their boredom.