They don't work well because the definition of "rape" keeps changing, unlike other crimes.
When I was in college, rape was forced sexual contact either through violence, threat of violence, or coercion.
Nowadays drunk sex makes you, the male, a rapist even if both of y'all are drunk.
You got chicks out here that intentionally tell a dude "no, not tonight" in the hopes that he will further pursue sex from her and if he hops up and bails he's a "lame". You have others that absolutely mean "no" when they say "no" and pushing the issue will get you an attempted rape charge.
Constant affirmation means if you don't stop and pull out the moment she says "ummmm..." instead of "yes" you're a rapist.
Some women welcome a pair of hands on her ass at the club while y'all are dancing. To others you've just sexually assaulted her.
There's entirely too many gray areas when it comes to rape and sexual assault made even worse by how one person may welcome things that another doesn't. That's why it's not working well aside from underreporting.
lol