There are many games with no story, or a paper thin one, that sell anyway because that is not their point. And Halo sells way more because of the multiplayer than the single player. If it was only SP, Halo would not sell nearly as many copies. If it had just MP, it would still sell a lot.
The thing that attracted me to JA was the lightsaber fighting. Sure, I hoped it had a great story as well, but the what differentiates it from JO was the lightsaber combat. That is what makes the game stand out.
I am always in favor of a good storyline, but some games don't really need them to be successful. Many MP FPS are like this.