I think the people giving this advice know enough psychology to know it works (defined as: likely to get people out of debt), and enough mathematics to know it's not optimal.
As to the people in debt: if they always consciously made (suboptimal) decisions, most of them wouldn't be in debt.
So the way to overcome conscious suboptimal decisions is to keep making more conscious suboptimal decisions? That is what I have been doing wrong... stupid me for trying to change.
Jokes aside, you are probably correct, I have always been torn between trying and failing to be perfectly rational versus doing suboptimal emotional things.
As to the people in debt: if they always consciously made (suboptimal) decisions, most of them wouldn't be in debt.