Familiarity, tons of features, existing well-worn supporting libraries for lots of languages and ecosystems, and depending on which one also safety/reliability

Familiarity, tons of features, existing well-worn supporting libraries for lots of languages and ecosystems, and depending on which one also safety/reliability and, for a variety of common query patterns including many that look pretty damn graphy, performance and predictability. FWIW my experience is with Neo4j.