Don't solve the problem, hide it.
"In a recent answer to a House of Lords question, the other place was told that in the 10 years to 2015, 250,000 appeals were allowed against the Home Office," - I suspect this may be part of the reason for the immigration data exemption. Instead of trying to make fewer mistakes, they're trying to make it harder for people to prove mistakes have been made.
The other factors in the reasoning are probably general anti-immigrant bias and government's apparent determination to hide all the data they possess, even as they slurp up everybody else's.
Biting the hand that feeds IT
