I think that commenters are assuming that dog walking is the benefit.
That’s a factor, but a few studies have shown association with a dog in a household (not ownership) has positive effect.
Companionship is a key factor with dogs and a key deficiency in many people. The human-dog relationship is unique because we snap into the dogs innate pack structure. Dogs want to take care of us, and that brings joy.
I’ve seen it with elderly folks and my own son. Our family dog made herself my son’s training wheels when he was learning to walk.
If not, you have a study showing that 'Dog ownership promotes regular healthy walking'.