I think that you will find that Sherbourne and ISLQ have quotas imposed by the government / SEC. In return they basically get free buildings and are controlled in so many ways by the government.

If you look at other schools, they don't have quotas and are not forced to teach as much Arabic or Islamic Studies.

These are supposed to be 'outstanding schools', but neither ISLQ or Sherboune are first division schools in the UK. Sherbourne is good, second division and ISL is just unknown - in the UK and internationally. It must be disappointing for the SEC that so far they have not managed to attract any really world class school. I think the issue is that these schools refuse to accept the level of control over curriculum and school fees.