Because childhood is a rare time in one's life where you have the freedom to enjoy the outside, and not have to sit in front of a screen. FWIW I don't think books are a good use of time either.
I guess childhood is a rare time where you have the freedom to loiter, but I guess this isn't really true anymore in the Western world, as it's a sure way to get your parents in trouble with social services, thanks to overzealous neighbours.
I spend plenty of time outside as an adult. How exactly do adults lose their freedom to enjoy the outside?
The beatings will continue until morale improves.