Except, of course, if it isn’t. There is nothing in these verses which demands ex nihilo.
Even AiG does not agree that “bara” is always creation ex nihilo. What books have you been reading?
This short study shows that there is no basis for saying that bara only means an instantaneous, out-of-nothing, supernatural creative action
AiG - Understanding Genesis 1 Hebrew: Create (bara) & Make (asah)
Given that man was formed from dust and woman was fashioned from Adam’s rib or side, it is plain that bara is applied here to creation from prior material.
Conspicuously absent is any qualification or extended verbiage of ex nihilo or out of nothing in the Hebrew text.