Why doesn't Bloodletter Curse maintain its madness passive?

I was comparing the gold efficiency between Bloodletter Curse and Black Cleaver, and Black Cleaver is just majorly more gold efficienct. Bloodletter Curse gold efficiency is improved a bit by getting riftmaker.

But I feel like it's kinda unfair that Black Cleaver provides like 30% Pen + an extra passive while being more gold efficient. Initially I was like considering the need for AP bruisers Bloodletter should also have an MS passive, but I think that might end up defeating the point of Cosmic Drive. That's when I realized that Bloodletter removes Haunting guise's madness effect (2% more damage per second up to 6%). I think that passive should be maintained, like for Liandries, and riftmaker, upon completing the item.