Gallia entered a completely seperate star cluster from Sirius. None of the four Sirian houses chose to settle there because they came upon Sirius first, and it seemed to them to be a perfectly acceptable place to settle. Basically, they wern't going to pass up a good thing just because there -might- be something slightly better up the road. Also, we must remember that the Gallic sleeper ship did not have to begin its journey in the same way as the other sleeper ships, in that it did not have to activate its hyperdrives after breaking through a blockade under heavy fire. The Gallics, who by the end of the Sol war were already beginning to suspect trechery from the other Allaince nations within the Sleeper ship project, were very careful to select a vastly diffrent rouit from the one that their Sirian counterparts had selected. Because of their aversion to landing in the same place as the Sirians, the extra time they were allotted to plan their course from Old Sol, and the fact that they traveled in space for much longer than any of the sleeper ships (The gallic sleeper ship arrived ~80 years after the Liberty landed, which, depending on the speed of a Sleeper Ship's hyperdrive, could mean they potentially traveled many lightyears further than any of the Sirius ships,) one can reasonably assume that they were able to reach a star cluster that the Sirian settlers thought was simply 'out of their reach.' The fact that the territory Gallia chose to settle had vastly more resources was just a concident, or perhaps the universe's sense of 'poetic justice.'
