I'm not quite sure what the source of the problem is, but I would suggest that it lies in the fact that one can have a career as a politician. Political parties are massive, power-hungry and monied machines that are largely unregulated (and, really, who would regulate them?) -- which is unlike any other massive, power-hungry and monied machine I can think of. (Even large corporations are subject to independent regulation.) If there were constant turnover of the higher-ups, then this would act as a check on their institutional ossification; but, there is no such turnover. Hence, we see the interests of the populace ignored in favour of the ongoing power interests of an elite -- and, worse, an elite whose claims to being elite are only grounded in their own self-interest.