The ones the DNC and GOP serve haven't changed, capital's interests have morphed depending on varying domesting and international situations. As for allowing multiple parties, on paper that's true, but not in practice. See the ways they fuck with PSL ballot access, such as in Georgia in 2024. Finally, the idea that voters fall into 2 large groups is a consequence of capitalism being divided into 2 dominant classes, proletarians and capitalists, but only having the parties represent the capitalists. It's political theater, not representation.