That's because our current system rewards politicians with money and power. Capitalism is driven by accumulation, this is a necessary function of the Capitalist mode of production. Once Humanity advances beyond it, representatives can be selected for without allowing them to amass Capital.
The power to do...what? That's the question. You can say that Bernie Sanders is only interested in power, and you'd be superficially correct. What he wants to do with that power would help people like me, and that makes all the difference.