Hep-C is very rarely sexually transmitted, it's strictly blood to blood.
"However, because of the high prevalence of hepatitis C, this small risk may translate into a
non-trivial number of cases transmitted by sexual routes. Vaginal penetrative sex is believed to have a lower risk of transmission than sexual practices that involve higher levels of trauma to anogenital mucosa (anal penetrative sex, fisting, use of sex toys)."
So, your observation is true, but if BBFS is on the table, a risk is there, and even moreso if BB anal comes into play.... which is not unimaginable since there is already BBFS to be had. There was a while back the infamous indie Thai SP who did both.
Still, there are numerous STDs, some potentially very damaging and some deadly, to be transmitted through BBFS... none of which appeal to me.
With the SP doing BBFS being a statistically more likely carrier of something versus a SP who always uses condoms, I can skip the higher risk and have my good time with a safer choice.