HCV spreads more easily than HIV through contact with infected blood. It is much more common in IV drug users than is HIV although no one can account for this yet.
Sorry I don't have a better answer for you. Epidemiologists are doing some studies to try and figure this out.
Because HIV is transmitted by sex and over years people have been practicing safe sex and knowledgeable about the transmission. There is still many people walking around out there who don't know they have Hepatitis C.
In the past you didn't get tested for Hepatitis C. Now it's recommended to baby boomers when visiting a doctor. Hepatitis C is a silent diesease. More often than not people don't know they have Hepatitis C for many years. HIV does start showing symptoms much faster than Hepatitis C. It wasn't until 1992 that screening begin for hepatitis C in our blood supply. There has been screening for HIV for some time.
There is also some concern in the hepatitis C community that people are not being as careful as they should protecting themselves because the newer meds are so successful. So the fear level about hep C has dropped a bit.
HIV was appeared relatively recently, in 20th century. But HCV, according to some studies, was appeared many centuries ago.
Majority of HIV-infected people without treatment would die from AIDS in relatively short time interval (5-10 years). But only minority of HCV-infected people (probably, 20%) would die without theatment from HCV-related complications during their lifetime. Thus, HCV-infected people may remain infective during decades of all their lifetime.