Why do people watch movies when books exist? They're different mediums for delivering a story.
I saw this thread and assumed you were talking about actual walking simulators like Firewatch or Gone Home, ones that don't really have any gameplay mechanics besides walking and interacting with objects. But from your comments you seem to be taking issue with games like God of War, The Last of Us and The Witcher which makes me think you're a little misguided as to what those games really are. Those games have a story but that's not the sole reason they're popular. They're all groundbreaking titles in their own right from a technical perspective, they just happen to have good stories because that makes them resonate with players even more.
It's like how a movie with a bunch great fight scenes and no story isn't going to resonate with audiences in the same way as a movie with great fight scenes and a story to tie it all together. It's an important part of the immersive experience for a lot of people.
This is an honest question, not a troll: what makes The Last of Us groundbreaking from a technical perspective? I played it and loved the story, but the gameplay was utterly boring to me. I got through the game entirely because I wanted to see the conclusion of the story and when the HBO show came out I was thrilled because it meant I wouldn't have to play a game I hated to see the story of TLoU 2.
It's been years, but my recollection is the game was entirely on rails, mostly walking and talking with infrequent bursts of quicktime events and clunky shooting. What was groundbreaking about it?
What was groundbreaking was the character and world building. Joel and Ellie feel like real people, with interesting backstories and relatable emotions. In the PS3 era, it felt ahead of its time.
Well, a movie and a book are quite different. I think OP’s point, right or wrong, is that a story-based game with minimal or no gameplay is very close to exactly what a movie is.