Prostitution ring also affects the entire college, and who is to say these girls are healthy? It's more than one girl being so stupid they're placing their sorority, and especially Sage as the head of it, in danger.
Seriously, it makes zero sense to just handwave it as "oh, the girls will just figure it out themselves" in one case if you won't in the other.
edit: to clarify, the zero sense thing being the MC is given option to bring up one of these things, but never the other. Whether it's actually worth mentioning it to Sage is another thing, it's fine to leave it to player's judgment/discretion.