That's because everybody knows deep down inside that being a leftist in the imperial core really only means you want social justice stuff, that leftists only realized organized labor even existed like 4 years ago and that even today they will distance themselves from organized labor at the drop of a hat if it's even vaguely insinuated by anyone that something they want is in conflict with any traditionally social justicey pet cause at all.
This is why leftists in America have such an easy time imagining the concept of "right wing socialists" but consider the idea of "right wing social justice advocates" to be paradoxical, because in America, being left wing is the same as being a social justice person.