All of what you mentioned looks like a possible contributing factor, but this one stood out to me:

> Or perhaps people who are less lonely are generally more knowledgeable/well-informed about these individuals.

I'd go as far as saying, people who are less lonely are more interested in those individuals in the first place. Celebrities are social objects. There's nothing inherently interesting in life or personality of any specific celebrity - what makes them interesting is that other people know about them too, so discussing them is a way to bond with others, have fun, etc. Lonely people do less of that, so they have less of a motivation to care about celebrities in the first place.

Yes, from the Discussion section of the paper:

> Prior work even finds that celebrities that generate common ground between strangers are disproportionately discussed in conversation, suggesting shared celebrity knowledge can provide a “foot in the door” to forming ties with others

Heh, I know that studying obvious things is the "bread and butter" of scientific study, but it's still funny to read sometimes...

"Hello, fellow coworkers! How about the local sports team, did you see them play last night?"