There are many factors that could make women stay silent when sexually abused. 1. Poverty: A lady from a very poor background may be unwilling to fire a case against any individual who sexually abused her. For instance, if the abused person is from a rich background, the lady who barely eat one square meal in a day, won't be that financially strong to take the case to another level.
2. Illiteracy: illiteracy can also be a factor. In most of the undeveloped countries in Africa. Women who are uneducated are subdue to accept any sexual assault that came from the opposite sex. Lack of education makes them not to know their fundamental right.
3. culture: women keep silent where it was noticed that culture has more influence on them. 4. Environment: Most women who have been a rap victims, may be so ashamed to speak up or report to the authority when raped so to avoid more insults from the society. They wouldn't like people to know about it and call them names even when it obvious that they were raped. People may still put the blame on them.
My answer would be stigmatism.Especially here in Africa. It would be pointed out by some parents that "Rachel was raped last month and no one has any idea what kind of person raped her orqhat kind of disease she has contracted so on and so forth. such sister could be rendered unmarried for a long time or even a lifetime.
Sometimes,the victim comes from a prestigious family.Speaking out after being raped will cause damage to her family so she keeps it to herself to protect her family's honor Some victims also stay silent because they are afraid; afraid of the person who raped them because he is influential and no one will believe them or afraid of the stigma and pity people will have in their eyes when they look at them