The shift from search engine to answer engine is the core change behind GEO. A search engine returns ten links and lets you choose. An answer engine reads the sources for you and returns one composed response, sometimes with citations, sometimes without.
This changes the goal of marketing. Ranking on page one matters less if the user never sees the page. What matters is whether the answer engine pulls from you, names you, and links you. Answer engines also tend to compress a category down to a few recommended options, which raises the stakes of being included.