It's obvious people intend to spend money when they have money, like a salary earner every month ending they just have the desire to buy much cause they have the money. They spend money on unnecessary things just to satisfy their desire. I think this are the common reasons why most people can't save their money, they lack financial discipline.
I personally, ever since the economy got so hard in my country I learnt how to manage my money, the urge to spend will always come but due to the economy I don't spend my money on things that are not necessary
I think the more income there is, the more there is to cover, I remember when I had a mediocre monthly income but on the way there was always enough and when there was a loss of additional income unexpected costs always appeared. So the assumption that people are not optimal in saving cannot necessarily be said to be so, however, perhaps there are several things that need to be addressed so that the desire to save is delayed. Everyone has a discourse there.