A lot of "traditional" white American food rises from traditions of using government issued foodstuffs. Government cheese, spam, various concoctions devised from military rations. But quite a lot also comes from what immigrant communities were able to afford, which was generally the worse stuff. There's also a not-insignificant number of white households that possessed no generational cooking knowledge because it was done by slaves, and thus had no culinary culture they could continue without the requisite skills.