As if walking briskly would make people with shitty lives and situational depression (like, tons, judging from statistics and related depression drug usage) happy?
Exercize is good for endorphins and depression, but let's not oversell it on inducing hapiness.
Walking at the sides of busy roads is very different from walking around a calm neighbourhood, or even a park, a forest or any other environment which is not high-density urban or industrialized, polluted and ugly roads.
The good options are inaccessible to a large part of the world's population during work week.
Therefore this study misses crucial factors and is an excersise (pun unintended) in absurdity.
Still, I also see some positive effects from Apple Fitness gamification even without the watch, and I'm privileged enough to be able to reach a park in 15 minutes.
Walking in American cities is awful, but if you live in a good country that limits vehicle access its super relaxing to walk around the city and see all the cool stuff going on.
No toxic fumes. No engine noise. No risk of sudden death. Just the low background noise of footsteps, chatter, people laughing, etc.
I know it's fun to hate on America but that's bs. We walk several miles in our city every day and it's great. We'll walk in state parks or near our cabin on the weekends but there's nothing wrong at all with walking in an American city.
Walking briskly and casually walking are very different activities.