Until recently, most publications didn't capitalize "white" or "black", but capitalized everything else ("Indian", "Native American", "Asian", etc.).
Recently, there has been increasing recognition that Black isn't just a (lowercase) skin color, but an identity like the rest and thus ought to be given the same capital-letter-recognition "Black". A large number of publications have made this change in the past couple years.
The reason "white" still isn't capitalized is because many people are uncomfortable recognizing white identity -- because in the past and still ongoing, that is often linked to white supremacism.
So as long as capitalizing "White" continues to carry (even unintended) associations of white supremacism, it's probable that most publications will keep it lowercase.
To be clear, I'm not expressing any opinions here as to whether this is right or wrong or desirable or not (edit: or even whether white identity exists). This is just a description of the reasons for things currently.