Honestly, I'm surprised that OP is being so obtuse about this. It's clear once you're familiar with intersectionality, but I think it could do well to be explained at least a little bit for those who aren't.

Essentially, the argument is that feminism, while a good force, needs anti-racism to maximize it's potential, just as it needs support for LGBTQ+ rights, since a lot of people are impacted by racism, homophobia, transphobia etc. Focusing largely on cis-het white middle-class women does help them, but we need those other elements too to be able to truly liberate people