open-world is about freedom and choice,
That is literally the appeal of an open world game, that’s where most of the meat and potatoes of the game usually lies.
One time a few years back, I saw this guy bitching that he had poured 200 hours into skyrim, and had never once encountered a single dragon, the guy never got far enough in the main quest for dragons to start spawning in and he had still put two hundred hours into the game.
That is literally the goal for open world games, that’s one of the reasons people love the elder scrolls games.
That is still different from a non-linear game however, non-linear games still don’t have giant worlds to explore but more confined routes dungeons and towns, you just more choice in what you do