This was a horrible case of a genuine false accusation. But Queen is right - the vast majority of reported rapes which don't lead to conviction either get "no-crimed" at an early stage (police decision) or the CPS decides they don't have a high enough chance of conviction, or, if it does get to court, the jury decides that the standard of beyond reasonable doubt has not been met.
People who've been on juries have said (re. a variety of crimes) that they may have been, for instance, 90% sure the accused did it, but 90% wasn't enough, because it had been spelled out to them that the threshold was reasonable doubt.
And that's before we get to the fact that occasionally you get juries where you suspect that "reasonable doubt" can be raised by excuses of the calibre of "alien space dogs from the planet zog ate my homework by travelling back in time to before the teacher had actually set it." I can't forget the dreadful case where the man used the defence that he had tripped and fallen penis first into the vagina of his drunken-to-the-point-of-unconsciousness underage partner who happened to be lying on the floor in precisely the right position to make this unlikely scenario play out as he described it... he was acquitted.