...because it's too positive.
The review on the impact of internal EU immigration (which is a huge issue with voters in the UK) was compiled by civil servants will report that the UK currently benefits from the rules.
This once again proves that the paranoia and worry about EU immigrant is nothing more than xenophobic fear and the need to blame someone. The government are happy to pin the blame for lack of jobs and economic growth on the EU and immigration when it's clear that austerity is the reason we have failed to see significant growth.
There are a million Brits living in the EU, yet no one ever seems to take that into account on the balance of immigration/emigration.