Possibly because they don't think these are crimes?

There are certain communities who the police refuse to name, but I suspect we know which ones who appear to be strictly law abiding in that the police have never been called out to deal with a problem with them. (Lack of) Honour killings, domestic violence, sexual abuse of children and female genital mutilations are some of the offences that are believed to be unreported in some communities.
Mail.

Parts of the UK are becoming no-go areas for police because minority communities are operating their own justice systems, according to the Chief Inspector of Constabulary.
The rise in ‘community justice’ means crimes as serious as murder and sexual abuse are going unreported – a situation reminiscent of Belfast in the height of the Troubles.
Tom Winsor said police officers were simply never called to some neighbourhoods, where law-abiding people rather than criminals administer their own form of justice
He said: ‘There are some communities born under other skies who will not involve the police at all. I am reluctant to name the communities in question, but there are communities from other cultures who would prefer to police themselves.
‘It’s not that the police are afraid to go into these areas or don’t want to go into those areas,’ he said. ‘But if the police don’t get calls for help then, of course, they won’t know what’s going on.’
Honour killings, domestic violence, sexual abuse of children and female genital mutilations are some of the offences that are believed to be unreported in some cities.

I suspect we now know which communities these are, but a big clue is that they begin with m and ends with uslim.
The problem being of course that (Lack of) Honour killings, domestic violence, sexual abuse of children and female genital mutilations are not crimes to many muslims (particularly the men) and so may not have been reported anyway and the community as a whole does not relate to our society via their traditions and their vile religion which tells them that it's ok for 53 year old perverts to have sex with nine year old girls. It also tells them that they can rape their enemies women, keep slaves and butcher anyone who offends them whilst demanding protection money from those who live in their midst. So in a closed off community, which is what many muslims aim for, such 'crimes' would never be reported anyway as that is the norm for many of them and they see nothing wrong with it.
That is unfortunately where the great socialist/liberal wet dream has left us, with whole communities cut off from the mainstream and encouraged to do so in the name of diversity, keeping traditions which in the modern world would rightly be condemned as barbaric.
Instead of being 'pulled' on such acts, any criticism is met with cries of 'racist' bigot' islamophobe...

A spokesman for the Muslim Council of Britain said: ‘We all rely on the police to protect our communities and this can be only done through full co-operation and partnership.
‘Co-operation is particularly important for Muslim communities who have experienced a rise in Islamophobic hate crimes.’

That rise being non-existent as the criticism of the Tell MAMA showed when such examples of islamophobia were shown to be mostly words on a computer screen or simply made up.
Until we have a level playing field with total integration, such crimes will carry on, no doubt about it, this is one of the dire legacies mass uncontrolled immigration coupled with multiculturalism and socialist (lack of) ethics where we're the racists never the immigrants/non whites.
And then they'll wonder one day why it all kicks off...