Money is quite possible for a person to be very rational, a lot of areas of life, and totally irrational in others. The political system indulges that because they have no incentive to vote rationally. Economists are not the median voter. Why don't we have more protectionism? Yes, that's a great question. And one that I address later in the book.
Bryan Caplan, of George Mason University and blogger at EconLog, talks about his book, The Myth of the Rational Voter: Why Democracies Choose Bad Policies. Caplan argues that democracies work well in giving voters what they want but unfortunately, what voters want isn't particularly wise, especially when it comes to economic policy. He outlines a series of systematic biases we often have on economic topics and explains why we have little or no incentive to improve our understanding of the world and vote wisely. So, it's not special interests that are messing things up but the very incentives that lie at the heart of a vote-based system. This is a disturbing and provocative lens for viewing political outcomes.