Because that quote is complete bollocks and utter lies made up to push some kind of "white people are being oppressed" culture war clickbait (the same that tries to align the GC movement with racist ideology on the grounds they are both anti-woke).
"while white writers must avoid writing about non-white characters"
Except one look at the best seller chart or a peek inside a Waterstones will show you that tons and tons of white writers write non-white characters without anyone raising an eyebrow or any "risk" of controversy.
The paranoia that white people are being oppressed or that non-white people are stealing what rightfully belongs to white people is sheer Enoch Powell.
"in a business which will not consider working with white male authors."
LOL. The vast majority of authors published are white men. The idea that the business "won't consider working with white male authors" is just racist MRA delusional fantasy pushed by Andrew Tate types.
It's really really alarming how quickly a thread in Feminist Chat, which ostensibly was about trans ideology and gender, has become about "white men being oppressed." White men are not oppressed.
I'm an author, not an employee of a publishing company.