> Sleep regularity may be a simple, effective target for improving general health and survival.

But why would it NOT be? Seems stupid for us to have evolved into beings that need our sleep to be irregular.

There are things that are causal and have little to no effect and things that are causal and have a large effect. I think determining whether and how much something matters, especially when the target audience is "all humans" is a worthwhile endeavor. So it may seem obvious to you, but many many important scientific findings were because somebody looked a little deeper at something that seemed obvious to everyone else.

Because for it to be effective it must have reasonable cost compared to the benefit. The cost for such a sweeping lifestyle adjustment seems quite high, and the authors have not showed any benefit to interventions.