It's so they can do the stuff they say they hate when other people do. Basically they're looking to justify their shitty behaviour.
"It's ok to hate white people because black people can't be racist"
"It's ok to burn down this neighbourhood because my anger is justified because I'm black"
"It's ok to segregate by race because we're trying to get justice"
"It's ok to force an unfair and incredibly biased law because we're trying to create equality"
They blame white people because it's the narrative, not seeing the low-key racism in saying that white people are responsible for everything and POCs are just helpless sheep caught up in the gravity well of Whiteness. Also, if you've spent the last ten years blaming all your problems on white people or excusing the shitty behaviour of a lot of very shitty people, you're going to have to admit you were wrong. Brianna's pride is what is standing in the way. She will never admit she was wrong and never ever ever admit that her whole world view has been wrong. This is true of almost all higher-up SJWs. They're tyrants, pure and simple. They're petty authoritarians and tyrants who want to force their will on everyone and do so with the approval of their own concious. This is why they hate it so much when any dares to speak against them. Every once in a while they might doubt themselves. They might see the light for an instant and be blinded by it, so they cover their eyes, plug their ears and scream until they've convinced themselves they are correct again.