Marxism has abandoned the working class for racial minorities because the workers were prospering too much under capitalism and so Marxists needed a new ‘oppressed’ group to save.
When Marxism was formulated in the 19th century, Western societies were, in general, racially segregated. Marx was a rabid racist, himself. But, after the 1960's, segregation was abolished. In other words, the playing field changed & Marxism adapted.