Because if you just sit at home all day watching T.V or on a device for 10 hours, It can be bad for your eyes and you don't get any Vitamin C from the sun.
It's good to get out of the house, because, When your outside you feel nice and refreshed when the wind hits your face, and you hear the birds tweeting.
I think its good if you have a loop or just getting out of the house each day and going for a walk around your neighborhood, or around your house. plus, Its good to be healthy.