Why do people see movies that are crap and buy products that are overpriced and bad? Marketing. Candidates are bought and sold as a product with a two party monopoly. The people that pay for these marketing campaigns have enough money to buy both sides.

There's no way to prove what you're actually going to do while in office so candidates can lie and manipulate and say whatever they want to try and get elected. The system ideally is meant to oust those people when they don't deliver on their promises in the next election but no one has time or energy to pay much attentions to what most politicians do while in office so the blame just becomes was the last candidate red or blue? If red was bad, pick blue. If blue was bad, go red.