Rapists know they'd be punished and/or shunned if they spoke of their crimes, so they don't talk about it.
Victims on the other hand are encouraged to seek help; talking through the trauma as a means of coping and healing.
It only makes sense the victim would be more commonly known about than the offender.
On top of that; a rapist is more likely to have created multiple victims, it's not just a 1:1 comparison.