E-E-A-T is not a single score you can set. It is a set of signals that tell systems your content is produced by people who know the subject, at an organization with a real reputation, and can be trusted. First-hand experience, named expert authors, citations from respected sources, and a transparent, accurate site all contribute.
For GEO it matters because answer engines prefer to ground and cite sources they consider reliable. Demonstrable expertise and authority make a model more comfortable pulling from you, especially on topics where accuracy is high-stakes.