It's the identity, stupid. After 1964, the Republicans became the party of white people and men, and the Democrats became the party of everybody else. Both sides talked about the economy, but neither side actually cared about economic class interests. They were more interested in protecting advantages (Republicans) and dismantling privileges (Democrats). That the economy was being hollowed out by globalization - importing meanness in the form of cheap goods - never occurred to anyone, because everyone likes cheap goods, right?