askchapo

I think it's because party discipline doesn't really exist in the US the way it does elsewhere. In the UK, if Labour drums out its popular elements, they can run off and form new parties and their popularity will travel with them. In the US, if you win, say, a Democratic primary, there's really nothing the Democrats can do to you until the next election cycle, and even then all they can really do is raise a ton of money for your opponent if they don't like you, they can't kick you out in the same way.

So there's a lot more heterodoxy within the two parties, and the alignments of the parties shifts much more over time. The most recent example of this is the Trump takeover of the Republicans, and the looming future of the Republican party being completely overtaken by millennial and zoomer Nazis. It's a far cry from what it was when Newt Gingrich lead the Republican realignment post Reagan/Bush.

In the past, I think the political machines that the parties all relied on lead to a different result because they had different mechanisms of forcing people out that they just don't have right now. The closest we've really seen to the Dems trying to actually enforce a party line was when they censured Ilhan Omar over Israel, a process which just showed how powerless they are in the current state of things to do that.

It's by design.

The second method will be exemplified in the federal republic of the United States. Whilst all authority in it will be derived from, and dependent on the society, the society itself will be broken into so many parts, interests, and classes of citizens, that the rights of individuals, or of the minority, will be in little danger from interested combinations of the majority. - Madison, 1788

By minority, he means the opulent one; rich people.

Any possibility of the Democrats falling by the wayside disappeared when they shifted to a platform almost entirely of progressive identity politics with economic policies of conservatives.

Good read on that shift is Listen, Liberal by Thomas Frank.

Other countries looked at the US's two party system when forming their democracies, and deliberately avoided that, through parliamentary systems or some sort of proportionate election.

I don't know the answer but I want to ask a second question that may get to the answer; has there ever been a first past the post representative republic that did have more than 2 healthy, viable parties?

americans are too easily distracted to build anything lasting longer than one election cycle and don't have any moral convictions to oppose media onslaught when they try.

The U.S. has a proud tradition of cranks and crackpots, who consistently either found the alternative party or are drawn to it.

Your country is too stable. You've been top dog for 100 years, once you are done with that you'll start cycling new parties like other liberal presidential republics