Why are the two American political parties so much more firmly entrenched than in other bourgeoisie democracies?

In highschool we were taught of "party realignment" to new voter preferences, where it seems in parliamentary systems they would just form new parties and let the old ones die off. (See the UK now)

It's not entirely due to the republican structure of government, because the US did cycle through a few parties before landing on these two. Republicans being deified for winning the Civil War makes sense but why did the Democrats not die out at least?