Maybe because extra-judicial “punishment” is unAmerican, no matter who it is.

I don't know, lynchings are kind of quintessential american.

In the United States, where the word lynching likely originated, the practice is associated with vigilante justice on the frontier and mob attacks on African Americans accused of crimes. The latter became frequent in the South during the period after the Reconstruction era, especially during the nadir of American race relations.[7] Black people were the primary victims of lynching in the U.S. (about 72% of the total), which was often perpetrated to enforce white supremacy and intimidate ethnic minorities along with other acts of racial terrorism.[8]

https://en.wikipedia.org/wiki/Lynching