because it's in my interests. I can see resentment and animosity towards white people becoming more and more widespread, more brazen and more publicly accepted. This will lead to all of my people's traditions and institutions and culture being destroyed and will lead to white people being marginalised and losing control of their homelands. When a people lose control of their homeland, that hasn't ever worked out well for them. So of course it is in my interests and in the interests of my descendents, my group to reject mainstream so-called "progressivism" and be a white nationalist. Which is infact simply pursuing my group's interests the way that every other racial and religious group pursues their interests and does so more vigorously and with more bias than white people. https://www.tabletmag.com/sections/news/articles/americas-white-saviors (see figure 2)
If you have several populations all of which have the same distribution of competence, but one of those populations is colorblind and individualistic and fairly meritocratic, while the other populations act with in-group preference and nepotism, and all these populations compete in the same job market for the same economic opportunities and positions of power , then the colorblind population will inevitably get outcompeted by the nepotistic groups who  will give a nepotistic, in-group preference advantage to each other by rating them slightly more highly for hiring and promotion.  When other groups have in-group preference, then you are at a disadvantage by not having in-group preference. Furthermore ,when you treat other people liberally and colourblindly  when they are infact favouring members of their ingroup and not acting colorblindly then you are being taken advantage of. You're being a cuck essentially.
This is why it is in white people's and everyone else's rational and justified self-interests to have in-group preference.