Something people are overlooking when they ask why the women didn't report their rapes:

the pressure most of them were under from family members NOT to report. Most families in years past would have seen being raped as a mark of shame -- something to hide from other people, not to expose in a trial. They wouldn't have supported their daughter in reporting rape; and in their pain and vulnerability, these young women NEEDED the support of their families.

And in the case of the alleged Cosby victims, many of them were being pushed by their own mothers to get involved with their rapist. Those same mothers who were so concerned about their daughters' careers would have put a lot of pressure on them NOT to report someone as powerful as Cosby.

Having said all that, no one should judge any woman for not reporting. It should be completely up to her, or else it is just another kind of violation. It is an enormously hard process and not all women are up to it or would benefit from the process.