Studies show incest victims rarely voluntarily agree to an abortion. The victims see the birth of their child as way out, because it will expose the illicit sexual activity of incest. It's also a chance to have a loving relationship that won't be exploitive.
The person committing the incest will often force abortion upon the victim to keep the crime secret. Unfortunately, other members of the family may also do this to avoide shame, etc.
I was responding to your claim about rape. You said nothing about incest in your original post.