In a first past the post system of districts with single representative candidates, it almost always resolves to two viable parties. That’s the way it’s been for basically all of American history.

The parties can change, but the shape of the system remains constant: a vote is only effective when cast for the largest opponent of your least desired candidate. It’s intuitive and discouraging.

The parliamentary systems used in much of Europe, for all their flaws, do allow for more robust and diverse representation.