An interesting article in the Washington Post referenced below states that:
The U.S. picks its elected officials in a way that creates a two-party system
Duverger’s Law says that the way a country’s electoral system is structured usually determines how many competitive parties that country will have.
Here’s how it works. First, when each district gets only one legislative seat (known as a single-member district, which we have in the United States) and, second, when the election’s winner takes that seat, then the system tends to have two dominant parties.
It's worth reading the entire article but the takaway seems to be that in order for a third party to win the two party candidates have to be caught on video kicking kittens or a third party has to play the long game by working districts and establishing coalitions.