I think the charge per hour aspect reflects the amortised cost of engaging in the activity. Books can be free if borrowed from a library - but ownership has an

I think the charge per hour aspect reflects the amortised cost of engaging in the activity. Books can be free if borrowed from a library - but ownership has an ‘hourly cost’ Mind sports like chess have an insanely low hourly cost, but regular sports that involve consumables like trainers have an hourly cost. Music is free if you sing, but otherwise involves buying and maintaining an instrument. Strings, for example are consumables.