First, if someone accepts an appointment, they are free to resign. They aren't required to stay for seven years.
Second, term limits are a good thing. You really have time to change and reform the organization, to leave your footprint, your ideas, and so on. If your mandate lasts only four years, that may not be enough, particularly if you want to amend the act or the code, since that requires a lot of time, consultations, and so on.
That means seven years is an asset. However, as you say—