Why it matters
A buyer asks a generative engine for the best food-grade chain lubricant for a bottling line. The engine does not hand back ten blue links. It reads several supplier pages, pulls the relevant specs, and writes one answer that names a few products and the distributors behind them. If your catalog page is one of the cited sources, you are in the answer the buyer acts on. If it is not, you are invisible, even when your part is the right one. That is the shift from ranking to being quoted.
Generative engine vs traditional search engine
A traditional search engine returns a ranked list and the buyer clicks through. A generative engine returns a written answer and cites a handful of sources inside it. The unit of competition moves from position on a results page to inclusion in the composed response. Same query, different surface, different thing to win.
In practice
Take a real cross-reference query like "replacement for Parker hydraulic filter element 924865." A distributor that publishes clean part data, the OEM equivalent, and the spec table on a crawlable page gives the engine something concrete to lift and attribute. A PDF datasheet or a price-gated SKU gives it nothing. The pages that get cited are the ones a generative engine can read and quote without guessing.