Sometimes the desire isn't to watch some specific show. It is to have the experience of sitting on the couch and watching something good on tv. This is why people channel surf, or scroll through netflix's collection. You want to have the experience of watching something. The goal is to be stimulated, to cure your momentary boredom.

I have the same experience with youtube, reddit and HN. I don't really know what I expect to see when I open the HN front page. If I knew, I'd navigate to that site directly. But I know I'll see something on HN. Maybe something that catches my eye.

Netflix is just the same. "I'm in the mood to watch a documentary. Let's see what they've got."