Why mostly people work just as they need and not a little more? There is an old saying; no boss can pay as little as I can work!

Probably because he biggest part of employees work because they have to work something/anything to pay the bills and for no other reason. There are no goals to achieve and no other motivation. Which means mostly people goes frustrated to there work and they came frustrated home. The result is ........ they work just as they have to work. If the manager or boss find a way to motivate the employees to make them understandable why this specific work is important for the company, community or what ever else, maybe there will be better result.