There are Managers that put themselves ahead of the company they work for. There are many managers like that. Perhaps if the result of the savings was more visible, or communicated, or at least an incentive not to spend the money was in place, it would make sense to those managers?

The problem wherever I have worked, is that each department gets a slice of the "pie", and there is always a battle for a bigger slice, rather than collectively growing a larger pie.