I do it because a) it's fun to play with stuff that you've personally had a hand in making, b) I love the star wars universe, and c) all of the other star wars games to-date have left me wanting so much more.
You have to really love modding to put in the time and dedication that it takes to put a total conversion mod together, like First Strike.
Most guys also have a need to create or build, and modding helps meet that need. Some guys, fix up cars, build models, remodel houses or even mod games.
What dawdler said and before I signed up the devs were taking too long they had been working on the mod for atleast a month, an entire month, maybe more! before I joined, I had to help speed up the process .