I'll try. Arieth delivers crabs like a huge factory to the entire college. DIK's suffered from this, so it's not an internal problem for HOT's anymore, it came out. If one of the HOT sisters is so stupid that she spreads venereal diseases and doesn't notice that she is sick, then I better warn Sage.
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.