Why isn't the word "white" capitalized when referring to the race?

Question

I was surprised to find that there's a growing convention of capitalizing the word "black" when referring to the race, i.e.:

A Black person.

I thought this was wrong, because I thought it was only proper nouns, like cultures, nationalities and ethnicities, that were to be capitalized. Black denotes a race, and nothing more, as there are many nationalities, cultures and ethnicities that fall within the black race. Calling black a culture or ethnicity would be reductive.

However, this capitalization rule apparently applies to race as well; see the 10th item here.

If this rule is in fact true, then that means black is to be capitalized when denoting a person of the black race. It also means that white is to be capitalized when denoting a person of the white race. Caucasian, which is a word denoting a race, is capitalized. It is a synonym to white.

So, if Caucasian is capitalized, and if people want black to be capitalized when referring to race, why isn't white supposed to be capitalized? Is white not a race? I'm no biologist, nor anthropologist, but if white is too genetically broad to be considered a race, then I'm pretty sure black would be too.

EDIT: As user Cascabel pointed out in the comments, Caucasian is derived from the Caucasus Mountains, which is a place, and therefore a proper noun. Therefore, regardless of what capitalization rules one employs, Caucasian has to be capitalized, and is therefore not necessarily an example of people capitalizing racial classification.

EDIT 2:

CMS have changed their preferred capitalization rules as of the 17th edition, which means that the answers to the linked post that this post was designated a duplicate of, are no longer valid.

Answer 1

One explanation for the discrepancy is offered by Nell Irvin Painter in their opinion piece for the Washington Post

These two identities don’t simply mirror each other — one works through a pronounced group identity [Black]; the other more often is lived as unraced individuality [white]. However much you might see yourself as an individual, if you’re black, you also have to contend with other people’s views. W.E.B. Du Bois summed this up as “twoness,” as seeing yourself as yourself but also knowing that other people see you as a black person. You don’t have to be a black nationalist to see yourself as black.

In contrast, until quite recently white Americans rarely saw themselves as raced — as white. Most of them, anyway. The people who have embraced “white” as a racial identity have been white nationalists, Ku Klux Klansmen and their ilk.

In July 20 2020 the following statement was released [emphasis in bold mine.]

NEW YORK (AP) — After changing its usage rules last month to capitalize the word “Black” when used in the context of race and culture, The Associated Press on Monday said it would not do the same for “white.”

The AP said white people in general have much less shared history and culture, and don’t have the experience of being discriminated against because of skin color. […]
CBS News said it would capitalize white, although not when referring to white supremacists, white nationalists or white privilege.

Some proponents believe that keeping white lowercase is actually anti-Black, saying it perpetuates the idea that whites are the default race.