Hear me out first.
This is not about if a story adds to a game or that a good story is always important. This is about what people want out of the game and what they focus on. Since open world games pretty much do everything possible to draw your focus away from the main story.
Also "main story" does not include the setting, characters and world which obviously is one of the most important things in such a game. It's just about the main story quest line.
I don't really give a shit about the main story in any open world game. Simply because I don't play those games for any kind of story. I play them to explore an open world. Discovering nice places, tiny little side quests which add to the world, beefing up my equipment and becoming stronger and finding the rarest items in the world.
I played Oblivion for multiple times and hundreds of hours without even touching the main story line. That's not because it is particularly bad or boring but just because it's just not that important for me. Oblivion is qactually a really great example for a proper open world game. Because most other open world games force you to advance the main plot just so you can explore more or get better stuff as an arbitrary wall.
So what do you think?
If you demand respect or gratitude for your volunteer work, you're doing volunteering wrong.