I’d say the idea was that certain events have happened in history. Broad strokes are known. But you’re running the simulation to find out the details. And that’s where the game happens. Reach the objective, whatever way, or fail. Much like any other game.
That may be some way away from a sandbox game but it’s worlds away from watching a movie.
But on rails games like Drakes Whatever? I’d watch the movie if it wasn’t annoying and full of obnoxious characters and bad script.
It’s happy compared to the alternatives you’re given.