For two reasons, first the work wears on you. It can lead to being cynical and it can be flat out unhealthy to continue to work at that level of government for a long period of time. The stress and pressure can be overwhelming. Secondly its good to get back out into the commercial field and have first hand experience with the state of the art. It means when you are talking to people about what it comes from a deep knowledge of what has been done and what was successful. Taking a break every half decade to refresh those skills is valuable.
Also that time limit really lights a fire under you to get stuff done. The people who are trying to use government services don't have years to wait for things to get better, their lives depend on things getting better today.
Also that time limit really lights a fire under you to get stuff done. The people who are trying to use government services don't have years to wait for things to get better, their lives depend on things getting better today.