My personal take is this is a consequence of the two-party system. In the US you can "identify" as a democrat or republican. Once you do that, you don't _have_ to think, you can let tribalism guide you.

If in another country I vote for these guys or sometimes those other guys, and once this little party that got a seat, but not really those ones, and I really hate these ones, then your "political identity" already has a lot of nuance. In Australia with preferencial voting, a single vote has a lot of naunce.

What can you get in America? Green Party supportors who "strategically" vote for a democrat? Not much else...

The other problem is the US has two parties: one center right (and i'm being generous with center) and another rabid right.

It has been like that since forever. They don't know how a left leaning party looks.