Or even better, why doesn't one politician start acting on actual principle? If you don't have confidence in a government, don't vote that you do. Period.
But if you want to be a pragmatist, fair enough, be a pragmatist. But then don't spend any time accusing other people of being bad for doing exactly what you would do. This is the whole problem with politics. Every party says "look what this other party has done, isn't it terrible!" Even when they would do something exactly the same or very similar.
People don't vote because politicians are just consistently and nauseatingly hypocritical. But unlike some patterns of behavior which are motivated by fear or addiction, this kind of behavior is easy for one to stop doing, just be principled about your pragmatism. .