For more useful info on this very problem, consult this other thread:

non-partisan approaches to politics

The reason politicians appear vacuous is this: They are tied to political parties which are the servants of major lobbyists (not of the public). They do not serve the public, yet they must appear to want to serve the public. This calls for a phony act that must be quite difficult for most people to pull off, unless they are natural born snake-oil salesmen. Accordingly, most of them sound vacuous. They are attempting to walk the narrow line that wanders between half-truths and outright lies. They are trying desperately to sound sincere, while serving a master who is utterly without scruples and only concerned about one thing: Victory.