All games need a story. Halo for an example is great not just because of the gameplay but because of the storyline. If it was just a normal shooter people would stop before they had to buy a whole new console.
A story is essential as it makes the game enjoyable and so makes it sell making the designer money. Win win.
The only reason JA sold is coz the rest of the Jedi Knight series had such good storylines.
Yes the saber fighting was amazing but lasted all of a month before wearing off on me.
Plus what were the designers doing after they'd made the engine.
Sometimes in life you're the pigeon. Other times you're the statue.