TL;DR: it's the two-party system.
Longer version: it's the two-party system. Yes, really.
Full version:
When Americans go to the supermarket, for every product they want to buy they are overwhelmed by choice. Cereals, tomato sauce, apples -- everything is available in all shapes and flavours, with multiple brands competing with each other and products coming from all over the world. I am writing this before the tariff-induced famine.
When Americans go to the polls, it looks a little bit different. There are, realistically for most of the country, only two options. This is a problem because when choice is limited, quality isn't incentivised. Going back to the supermarket example, imagine that there are only two brands of cereals you can buy: well, that isn't really a lot of options, and you might very well end up buying the cereals that you "dislike the least" rather than the ones you "like the most". As if that was not bad enough, the only two brands of cereals on the shelf are neither competing very hard on price nor competing very hard on quality. All they have to do to sell their product is avoid becoming too much worse than the competition and occasionally promise to cut taxes or cancel student loans.
It would be very different if the shelf had 10 brands of cereals, each competing for the best place on the shelf, the lowest price, the best flavour, and the highest amount of corn syrup healthiest ingredients. Competition makes for good products (and with that, we'll leave the cereal analogy behind).
The Republican and Democratic parties don't have to fight very hard for votes. In most cases they can rely on a loyal base of supporters who would swear allegiance to the party on their life, and anyway the US electoral system (with first past the post and the electoral college) doesn't exactly encourage political fragmentation: the two biggest parties simply get to play the electoral game undisturbed. When parties don't have to work hard for votes, the overall quality decreases, because all a party has to do to win some votes is to not suck too much. I am aware of the irony of me writing this while the current US president is probably tweeting his latest mental meltdown on Truth Social. But in THEORY, and for most of US history, the two-party system has worked against the interests of US citizens because when choice is limited, quality isn't incentivised.
Having multiple parties has another advantage: extreme positions by either 'big party' tend to be avoided. Imagine a country with multiple options: introducing... ✨the rest of the democratic world✨. If one party starts going off random extremist tangents like "we will put 145% tariffs on country XYZ" or "public debt is a social construct, let's just print more money and see what happens", then chances are that more moderate parties would gain votes, pulling back from the edge of insanity the parties that are drifting away from the centre as a consequence. Parties closer to the centre are often smaller, but tend to grow in size when bigger parties make political mistakes: it is important for voters to have a "plan B" to vote for rather than voting for the completely opposite party, which most people aren't willing to do.
So is that it? Should the US just change its political system altogether, abolish the electoral college, introduce more parties, get rid of first past the post, limit the power of executive orders, tax people fairly, repay the debt, and fund the education department until the percentage of people believing the sun revolves around the earth falls below 25%? Well, yes.
One last thing: having too many parties has its downsides too. Ungovernability is a big concern for countries (like the Netherlands) where the political spectrum is split into 8 (or whatever) parties. Coalition governments become the norm (which isn't necessarily a bad thing), and to be fair many of those parties have a lot of things in common anyway. But for sure a better system than the one being used in the US exists, and no, I don't care about what the founding fathers had to say about anything. Bye.
