Ok, I read the article. But I still don't know what the big lie is.
I think the big lie is that wellness companies, doctors, and sleep widget salespeople claim that you can improve your sleep with blackout curtains, less screen time, exercise, fancy tech, and a host of other strategies. But this article is saying that being healthier and richer improve your sleep more dramatically, and those are things that are not directly in your control.
Either that or, apparently, living in Nebraska or Minnesota