Just a theory...
After the somewhat slow paced Peragus, it needed something with a little action. Stage left, the mini games.
Pazaak is out of the question at this stage, as well as swoop racing.
That leaves the turret game. Since a shoot out, OK Corral style in space is unlikely to leave any survivors, considering the nature of Peragus and it's satellites (Sp?), they went for some nice safe indoor duck shooting
It doesn't make sense from anything but a pacing perspective really (or I've missed something completely). I didn't really like turret games, but it was nice with something else after endless metallic corridors fighting unchallenging mining droids.
Edited to add: It could be rationalised, that Sion brought cloaked assassins onboard and once the original crew was killed off, he picked up grunts as reinforcements somewhere along the way. They might also be spearheading an assault on Peragus and saving his precious assassins for more suitable tasks.
All guesswork though