Because the kinds of people who want you to distinguish between the two are the kinds of people who lie in the middle of the venn diagram. Which, to be honest, if it's not a single overlapping circle, it's pretty darn close...

Nobody wants to have their own nation state dedicated to their race because they appreciate other cultures and want them to live on their own.

Find me the white nationalist who is not a white supremacist, and I will have them demonstrate being a white supremacist to you.