Two different retrieval mechanisms
A Google search and an AI answer look similar from the user side: you ask a question, you get an answer. The underlying retrieval is different enough that the same page can dominate one and be invisible to the other.
Google retrieves by inverted index plus ranking. It matches query tokens to an index of pages, scores them on hundreds of signals (backlinks, engagement, freshness, authority), and returns ten ranked links. The user picks.
AI answer engines retrieve by embeddings plus re-ranking plus synthesis. The engine converts the query to an embedding, retrieves a set of candidate sources, re-ranks them using both similarity and authority signals, and composes an answer that quotes or paraphrases a small subset. The user never picks.