Employee engagement is lower with newer employees than employees who have been employed longer. It seems that new employees, who just have started their careers,wait to see which way the wind blows to see if their expectations are met (which has no negative effect on their productivity).
As the employment progresses, sometimes it becomes clear that the organisation can no longer meet the expectations, or that processes and bureaucracy temper the enthusiasm.
The employees, to whom this happens, will leave. The employees, who have little or no expectations to adjust, remain with the organisation. With the latter group; employee commitment, involvement and motivation increase as the years progress.