In this competitive world, even good friends in company will actually backstabbing you behind as you never knows... Smile in front of you but shows all the anger when you get promoted or huge increment.......

As everyone fighthing to climb the ladder, if you stay late... Your "competitors" will let everyone knows that you are not productive/efficient, If you go back too early although you finish all you work, "competitors" will "think" you lazy eventhough they knows its not......

Nothing is fair in this cooperate world.... From my very own opinion, Workers would stay late in company is because:

(1) OT Claims/Allowances (Extra Income)
(2) Company Culture
(3) Awareness and visibility to other co-workers/managers
(4) Something to learn ( valuable knowledge that will be priceless for next job hop)
(5) Too many jobs (overload) but you dont want to pass to other people, you owned more, do more, get more kind of philosophy.
(6) You dont like to go back, you feel that staying in office is better ( I have many of this kind of friends, wonder why... ).