Scope may have something to do with it too. If you have a small game that feels small, with a limited number of levels, I think that'd be okay. But if you have a huge game with awesome, professional-looking graphics, you might have some problems as you'd be seen as competing with Lucasarts.
I doubt Lucasarts would accept any contributions from a "nobody". That's not an insult to you, but reflects the way they would see anyone not established in the game industry.