Patriarchy and bias in the law.
It seems biased, seeing as though rape is generally targeted at women. The way the law is now, it favors the rapist over the victim, the former usually being male and the latter female. Lay low long enough and your crime just goes away. It's a sprout from the tree of rape culture and male patriarchy that needs to be pruned.
On the contrary, men have a greater chance of being murdered, but no statute of limitations on that.