Vorlon, I think you majorly overestimate the desire to fill the galaxy. How much would a civilization advance in the time it takes to fully make use of the resources in a single solar system? A lot! From the perspective of beings who have self-directed their evolution and become hundreds of times (at least) smarter than us, blazing across the galaxy with the intent to exploit it may not seem like a worthwhile enterprise at all. They wouldn't need to and they probably wouldn't be so insecure to feel an urge to expand just for the sake of expansion.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
Albert Einstein
Albert Einstein
