alt Hacker NewsBeyond that, a quirk of the American system in many states is registering your party affiliation at the time you register votes so that you can participate in primaries. When you've got >45% of registered voters identifying as being a supporter of one of the major two parties closely enough to add it to their name on the electoral roll, it's not exactly an encouraging environment to break that status quo
Other majoritarian democratic systems often also converge into two party (or two and a bit party, or two parties per region systems) but few seem to normalise voting for the same party every time in quite the same way.
To further add to that, many states do closed primaries. If a voter isn't registered with one of the two ordained parties, they realistically cannot participate in primaries at all.
If there would six parties to choose from, for example, I think it would be hard to argue that closed primaries are harmful. But since we have a duopoly, they exclude a significant portion of the voting population from participating until late in the process.