The standards of reelection should be higher than the standards for the first election. If someone doesn’t meet your standards, give someone else a turn.
There’s still a chance he’ll be better, whereas for the most part, the incumbent has already proved himself unworthy but still wins on name recognition.
Your POV has merit, but like most things, there is a sliding scale.
If the other guy is an <i>apikores</i>, would you choose him over an incumbent who didn’t fulfill all his promises?
Also, you know well that humans are built in the image of the Almighty, but indeed there is but one G-d. Ergo, every human is imperfect and cannot be expected to fulfill all his promises, even if his intentions are good.