Earlier quoted context omitted.
If they have 8 hours of work time and finished their tasks in 6, does that mean they have exhausted their usefulness to the business? Why not spend these 2 hours doing some small miscellaneous tasks?
Often lack of infrastructure, or communication about what needs doing. Traditional businesses are poorly documented, and not transparent, so knowing what you might do and how is often extremely difficult.
i.e. Lack of leadership