Pork barrelling requires one of the following to be an effective vote-buying strategy.

• There must be ways of subsidizing in which the special interest group knows they have received the benefit, but in which the rest of the population don't know that the subsidization has been given (or at least how much subsidization is given); or
• The population must be ignorant enough to think that if everyone is subsidized everyone can be better off. A little thought should convince any logically minded individual that taking a dollar off everyone, only to give it back to them in subsidies cannot possibly make them better off, even if there were no dead-weight losses, administrative overhead or corruption.

Most politicians in social democracies rely on a carefully crafted combination of these. Some subsidies are justified on economic grounds ('the government can invest your money better than you can'), others on humanitarian grounds ('but it costs us so little, and we can help so much'), and others on equity grounds ('these people pay so much taxes, they are entitled to a little subsidization to even it up a bit').

And the voters let them get away with it.