If a forest is changed to optimize output of a single species of plant or wood, then the forest as a whole is generally less diverse, resilient, and productive over the long term. Programs are physical. Because of this, systems can be sustainable. Programs cannot be. They are constrained by the laws of thermodynamics.
Systems are the only source of resources.
They are the only source of profit and wealth. Programs are merely channels for the expenditure of resources generated by systems. Systems can be self-regulating. For example, consider cybernetic systems like the human body such systems rely upon a limited number of inputs and adjust their operations to optimize the use of these inputs. Programs always require external regulation, and there are no inherent mechanisms to regulate programmatic operations.