Just noticed...
I'm currently rewatching Bleach, specifically the Turn Back the Pendulum arc, and I just noticed how most—if not all—of the captains that were sent to investigate in Rukongai are commoners (Kensei, Hirako, Rose, Love), while the ones that were left in Seireitei are nobles, like Yoruichi (and Urahara by extension), Kyoraku, Ukitake, an Kuchiki Ginrei. Unohana, though not a noble, was ordered to stay behind because they cannot afford to lose the head of the 4th Division.
Not sure if that's intentional but if it is, the reason can be either of the two. Or both.
1. Because the nobles are practically the founding fathers of Soul Society, the system was designed to protect them.
2. Strategically speaking, Yamamoto could've sent them to Rukongai precisely because they are commoners and are more knowledgeable of the area.
