I've also seemingly paradoxically found that scarcity seems to have a dramatic effect on this.

Immersion, the sense of losing hours to a good book (or a good movie, or video game, etcetera) I seem to find more difficult as availability increases. There's a constant nagging feeling that I could be making better use of that time, that perhaps the next book on Gutenberg would be 'better' (whatever that means).

It's very difficult to really pin down why that is. If I were fantastically wealthy and could buy books by the truckload without even thinking about it, would I feel detached from them all in the same way?