Rank to qualify, answer to be quoted
Retrieval draws heavily on the existing index, so classic SEO still gates candidacy: pages nowhere near ranking rarely get cited. Selection among candidates then favours passages that resolve the specific sub-question directly and stand alone when lifted, whose facts corroborate across other sources, and whose structure makes the relevant part unambiguous. That is why a position-three page full of hedged marketing prose loses citations to a position-seven page that simply answers the question in two sentences.