These are easy to implement, they are proven medically, and they have tons of other benefits for heart health etc.
How are you supposed to exercise if you're already suffering from SAD? How much of the perceived benefit from walking comes from sunlight exposure? What about climes where there are extended overcast periods with no direct sunlight for weeks at a time?
Any claim of "you can't do X until you did Y first" is of little value to people who have adequate motivation or resources to do X but not to do Y. Maybe doing X will make it easier to do Y later.
In fact, this is the exact approach I took; one of my motivations for starting an automation startup years ago was better lighting for myself, and that better lighting later made it easier to exercise more, start swimming regularly, etc.
Creating a startup to treat a mood disorder is a very roundabout way of doing things.
My main objection to rsync's comment was the flippant dismissal of people with actually diagnosed depression ("not interesting" were the exact words).
In response to your present comment, I would say that people who find themselves trying to invent solutions to their problems have likely already found the medical establisment to be less than helpful.