That's simply not the case. One needn't be a politician to spend more than one earns. It's just that for politicians spending someone else's money is way fucking more simple than spending their own. Almost zero thought goes into whether we as a nation want or need most of the shit we re-distribute our money on.
Remember govt. isn't in the business of making money, it's in the business of re-distributing what YOU earn. And let's all remember the wise words of the last moron in that office... at some point you've made enough. Lucky for us there are smart folks like him to decide for us what that point is.