Are they really watching, or is the TV just on in the background while they do other stuff?

At 42+ hours a week I'm no longer sure it matters.

I think for retired people, there mostly isn't all that much other stuff to do.

I am not retired, but my wife is. She does watch TV, an hour or two at night. She gardens and volunteers. Various acquaintances who have retired engage in volunteer activities: helping other seniors during health-plan "open season"; organizing free dental clinics in poor counties in Virginia; teaching and tutoring; even making sure that there are bags available for dog-walkers.

I would hope to be like that myself, but looking at my parents they did basically nothing after retirement (especially my father, my mother kept an active social life).

There used to be

There still is.