No, the reason the reporting rate is high but the prosecution/conviction rate is low is fairly simple.
You see someone who appears to have undergone it, you are as a medical professional (from memory) legally required to report it.
That means that every time someone is found to have undergone it, it's reported*.
Now the problem with prosecuting, let alone getting a conviction (remember that whole thing of having to have a trial and convincing a jury you've got the right person, yes it's a nuisance I know), is that unless it's new (IE still healing, or bloody) you've got a crime that might have occurred months, or years ago, depending on how often the girl has had a gynaecological exam, and IIRC they don't start doing that as a regular thing until the girl is something like 10 or 12 and is nearing/hitting puberty, as it's not something a doctor routinely checks in young girls, nor is it something that is seen by the likes of teachers etc (unlike say bruising from a beating), which means you've got a criminal act but effectively no idea who actually did it, and unless you can get the victim to ID them you don't have anything to start building a prosecution on, unless when you ask family members one of them pipes up "why yes I did it" or similar.
It's basically something that is as hard to get the victim to speak up about as other forms of physical abuse by the family, but because it's affecting the genitals the there are none of the sighs that often result in an investigation after reports by most professionals, or neighbours the child has contact with, so it's either a report by the victim, or the doctor/nurse after a specific type of appointment (so not even something a doctor will be checking when they go in for say a sore throat).
*or should be, and given the numbers is getting reported routinely when spotted.