I've been trying to put my finger on what's so particularly infuriating about this, and I think I've managed to figure it out: it's the liberal idea that oppressed groups contain that as some sort of innate feature of themselves, as if someone's experience is a direct deterministic result of their gender or skin color instead of a result of how external systems of power treat them and people like them using those characteristics to single them out or fit them into an arbitrary hierarchy enforced with terroristic violence. It's why liberals will equivocate a black man from an affluent background with all PoC, or point to black bourgeoisie supporting the police state as evidence that most PoC actually want more police violence (I've literally seen this exact argument, pointing to a survey of black business owners in NYC and only business owners as evidence that the drug war was actually overwhelmingly popular in black communities).

I don't think it's entirely even the way liberals don't understand what class is or how it figures into the systems of violence that uphold liberalism, it's literally just not understanding that the oppression of PoC is a result of generations of terroristic violence and exclusion by the white supremacist state and that the sort of oppression can be inflicted on anyone for any reason. It's like how they don't understand patriarchal systems beyond individual chauvinists, leading them to equivocate affluent and powerful women who ignore the abuses their male peers commit against less privileged women (like, golden fucking example right here: Hillary Clinton, who went above and beyond smearing her husband's victims as members of a partisan conspiracy) with all women, or unironically cheer on diverse representation in the leadership of systems that exist for the sole purpose of inflicting violence against people in the periphery.