My take: the zero-sum game is not solely about people having a fixed entertainment budget in purely financial terms -- incomes go up and down and it depends in the aggregate on the economic cycle. Rather, people have a fixed entertainment budget in terms of leisure hours per week that want filling. You can get a pay rise, but you can't get 5% more hours in the week than the 168 that your clock gives you.
Another issue is that some recreational products are rivalrous of time; you can't read a book and play a computer game simultaneously, or combine one of those with doing the ironing or cooking dinner. You can watch a video or listen to music while you're doing something else. Oh, and some products are use-once, while others are use-many-times (and in some cases this varies from individual to individual: do you re-read books, or read them once and discard?).
TL:DR; There's a zero-sum game in the picture but nailing it down is a whole lot more complicated than it looks at first sight.
Another issue is that some recreational products are rivalrous of time; you can't read a book and play a computer game simultaneously, or combine one of those with doing the ironing or cooking dinner. You can watch a video or listen to music while you're doing something else. Oh, and some products are use-once, while others are use-many-times (and in some cases this varies from individual to individual: do you re-read books, or read them once and discard?).
TL:DR; There's a zero-sum game in the picture but nailing it down is a whole lot more complicated than it looks at first sight.