A variety of things come into play here.

The police (whatever your confidence in their competence) make assessments as to whether or not there is enough that they are hearing from the accuser to get a conviction.

People also are unaware of what it is that they are saying, and how the listener will interpret it..

"so you are saying that you and your boyfriend of 5 years do this (given activity) every Saturday night, but this time you want to place charges, because this was different. How?"

Most police officers would realize a good defense attorney would destroy a witness like this. The accuser will most definitely walk away, feeling the system let her down, but the courts cannot act on feelings, only on evidence.

As the Ghomeshi trial showed, are we hearing all the story? What happened afterward? Was there surrounding information the accuser is downplaying, or ignoring, but are in fact major deterrents to pursuing police activity.

And finally, is the author telling us everything?