I have posted a few times on why pork exists, but it turns out my theory was wrong. I recently found this paper (link to non-gated), which shows empirically that politicians do not seek pork because pork directly gets votes. The paper supports the theory that politicians sponsor pork because it gets them financial support (presumably from pork recipients, such as contractors):

I found that money, not pork, is the main resource that sustains politicians’ efforts to maintain their personal-vote support base among voters. Deputies thus do not deliver pork because it provides a direct electoral payoff, they do so in order to gain the financial support of powerful economic interests. The money that comes from pork-barreling then helps them win votes.

Retrospectively, this theory is much more convincing than my theory. While it is difficult for voters to get information about pork spending, it is trivial for specific companies to know about pork directed at them. This theory is also more consistent with altruistic voters.

With this logic, Proportional Representation (PR) may not eliminate pork, as I suggested before, because politicians always have incentives to seek money to help their election. PR might still reduce pork spending for two reasons. First, as I have discussed before, money should have a smaller impact in PR electoral systems than winner-take-all systems. Second, in PR electoral systems, parties compete mostly with other incumbent parties, not outsiders, so the electoral advantage to individual incumbent parties should be a good deal smaller than in winner-take-all systems.