Yeah well, it's the United States, it wouldn't be the USA if people didn't sue each other for stupid reasons.
Like this guy who sued McDonalds for making him eating fat stuff. Gee, if you know it's fat, stop eating at McDonalds...
But anyway, did your friend had a certain history of false accusations of raping? That could cause the inaction of the police. Other then that, I dunno why they didn't act.