Most of the major authors are white currently. They may not feel comfortable expanding outside of their own homogeneous comfort zone because there is a very real chance they’ll be told they’re culturally appropriating, or they’re unqualified to write the experience of a POC would have. Also there are many POC that don’t want to read about “their” people written by a white author, they also want the author to be a POC not just the characters. At this point it is obvious that with a few very well known exceptions it is extremely difficult for authors of color to break into mainstream publishing companies especially in genres like Sci-fi and Fantasy. It does seem like there are more authors of color in general fiction and romance. Readers (especially white ones) have to prove they’re open to both characters and authors who are POC. Indie and self publishing have made it easier to access a more diverse author base but there’s a long way to go.