>I don't see how sleep regularity is a factor you can change as willingly as visits to the fridge

In some cases it might be hard (e.g. insomnia), in others it might be as easy as e.g. changing your schedule, or stopping binge-watching/gaming/doomscrolling late, or some such change.

>It could also just be that I find a treatment of symptoms to be less desirable than causes.

It is more opaque.

But the point is not that it's necessarily easy. It's rather than even if X -> Y is mere correlation, by forcing yourself to fix X (even if hard), the resulting changes might also help with Y.

And technically "bad sleep" here isn't necessarily a symptom either. It can be a co-effect of the same symptom.